. Update the Copyright year (only) when changing content.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.90"
+.set previousversion "4.91"
.include ./local_params
.set ACL "access control lists (ACLs)"
An &"easier"& discussion of Exim which provides more in-depth explanatory,
introductory, and tutorial material can be found in a book entitled &'The Exim
SMTP Mail Server'& (second edition, 2007), published by UIT Cambridge
-(&url(http://www.uit.co.uk/exim-book/)).
+(&url(https://www.uit.co.uk/exim-book/)).
This book also contains a chapter that gives a general introduction to SMTP and
Internet mail. Inevitably, however, the book is unlikely to be fully up-to-date
.section "FTP and web sites" "SECID2"
.cindex "web site"
.cindex "FTP site"
-.new
The primary site for Exim source distributions is the &%exim.org%& FTP site,
available over HTTPS, HTTP and FTP. These services, and the &%exim.org%&
website, are hosted at the University of Cambridge.
-.wen
.cindex "wiki"
.cindex "FAQ"
As well as Exim distribution tar files, the Exim web site contains a number of
differently formatted versions of the documentation. A recent addition to the
-online information is the Exim wiki (&url(http://wiki.exim.org)),
+online information is the Exim wiki (&url(https://wiki.exim.org)),
which contains what used to be a separate FAQ, as well as various other
examples, tips, and know-how that have been contributed by Exim users.
-.new
The wiki site should always redirect to the correct place, which is currently
provided by GitHub, and is open to editing by anyone with a GitHub account.
-.wen
.cindex Bugzilla
An Exim Bugzilla exists at &url(https://bugs.exim.org). You can use
this to report bugs, and also to add items to the wish list. Please search
first to check that you are not duplicating a previous entry.
-.new
Please do not ask for configuration help in the bug-tracker.
-.wen
.section "Mailing lists" "SECID3"
the Debian-specific mailing list &'pkg-exim4-users@lists.alioth.debian.org'&
via this web page:
.display
-&url(http://lists.alioth.debian.org/mailman/listinfo/pkg-exim4-users)
+&url(https://alioth-lists.debian.net/cgi-bin/mailman/listinfo/pkg-exim4-users)
.endd
Please ask Debian-specific questions on this list and not on the general Exim
lists.
.cindex "HTTPS download site"
.cindex "distribution" "ftp site"
.cindex "distribution" "https site"
-.new
The master distribution site for the Exim distribution is
.display
-&*https://downloads.exim.org/*&
+&url(https://downloads.exim.org/)
.endd
The service is available over HTTPS, HTTP and FTP.
We encourage people to migrate to HTTPS.
-The content served at &'https://downloads.exim.org/'& is identical to the
-content served at &'https://ftp.exim.org/pub/exim'& and
-&'ftp://ftp.exim.org/pub/exim'&.
+The content served at &url(https://downloads.exim.org/) is identical to the
+content served at &url(https://ftp.exim.org/pub/exim) and
+&url(ftp://ftp.exim.org/pub/exim).
If accessing via a hostname containing &'ftp'&, then the file references that
follow are relative to the &_exim_& directories at these sites.
If accessing via the hostname &'downloads'& then the subdirectories described
here are top-level directories.
-.wen
There are now quite a number of independent mirror sites around
the world. Those that I know about are listed in the file called &_Mirrors_&.
.endd
where &'n.nn'& is the highest such version number in the directory. The three
files contain identical data; the only difference is the type of compression.
-.new
The &_.xz_& file is usually the smallest, while the &_.gz_& file is the
most portable to old systems.
-.wen
.cindex "distribution" "signing details"
.cindex "distribution" "public key"
&_nigel-pubkey.asc_&. All keys used will be available in public keyserver pools,
such as &'pool.sks-keyservers.net'&.
-.new
At time of last update, releases were being made by Jeremy Harris and signed
with key &'0xBCE58C8CE41F32DF'&. Other recent keys used for signing are those
of Heiko Schlittermann, &'0x26101B62F69376CE'&,
and of Phil Pennock, &'0x4D1E900E14C1CC04'&.
-.wen
The signatures for the tar bundles are in:
.display
&_exim-postscript-n.nn.tar.gz_&
&_exim-texinfo-n.nn.tar.gz_&
.endd
-.new
These tar files contain only the &_doc_& directory, not the complete
distribution, and are also available in &_.bz2_& and &_.xz_& forms.
-.wen
.section "Limitations" "SECID6"
version.
This code implements Dan Bernstein's Constant DataBase (cdb) spec. Information,
the spec and sample code for cdb can be obtained from
-&url(http://www.pobox.com/~djb/cdb.html). This implementation borrows
+&url(https://cr.yp.to/cdb.html). This implementation borrows
some code from Dan Bernstein's implementation (which has no license
restrictions applied to it).
.endblockquote
acknowledgment:
&"This product includes software developed by Computing Services
-at Carnegie Mellon University (&url(http://www.cmu.edu/computing/)."&
+at Carnegie Mellon University (&url(https://www.cmu.edu/computing/)."&
CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
described in more detail in chapter &<<CHAProutergeneric>>&.
.ilist
+.cindex affix "router precondition"
The &%local_part_prefix%& and &%local_part_suffix%& options can specify that
the local parts handled by the router may or must have certain prefixes and/or
suffixes. If a mandatory affix (prefix or suffix) is not present, the router is
.vindex "&$local_part_prefix$&"
.vindex "&$local_part$&"
.vindex "&$local_part_suffix$&"
+.cindex affix "router precondition"
If the &%local_parts%& option is set, the local part of the address must be in
the set of local parts that it defines. If &%local_part_prefix%& or
&%local_part_suffix%& is in use, the prefix or suffix is removed from the local
If your operating system has no
PCRE support then you will need to obtain and build the current PCRE
from &url(ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/).
-More information on PCRE is available at &url(http://www.pcre.org/).
+More information on PCRE is available at &url(https://www.pcre.org/).
.section "DBM libraries" "SECTdb"
.cindex "DBM libraries" "discussion of"
.next
To complicate things further, there are several very different versions of the
Berkeley DB package. Version 1.85 was stable for a very long time, releases
-2.&'x'& and 3.&'x'& were current for a while, but the latest versions are now
-numbered 4.&'x'&. Maintenance of some of the earlier releases has ceased. All
-versions of Berkeley DB can be obtained from
-&url(http://www.sleepycat.com/).
+2.&'x'& and 3.&'x'& were current for a while, but the latest versions when Exim last revamped support were numbered 4.&'x'&.
+Maintenance of some of the earlier releases has ceased. All versions of
+Berkeley DB could be obtained from
+&url(http://www.sleepycat.com/), which is now a redirect to their new owner's
+page with far newer versions listed.
+It is probably wise to plan to move your storage configurations away from
+Berkeley DB format, as today there are smaller and simpler alternatives more
+suited to Exim's usage model.
.next
.cindex "&'tdb'& DBM library"
Yet another DBM library, called &'tdb'&, is available from
-&url(http://download.sourceforge.net/tdb). It has its own interface, and also
+&url(https://sourceforge.net/projects/tdb/files/). It has its own interface, and also
operates on a single file.
.endlist
However, some of the operating systems that supply &[iconv()]& do not support
very many conversions. The GNU &%libiconv%& library (available from
-&url(http://www.gnu.org/software/libiconv/)) can be installed on such
+&url(https://www.gnu.org/software/libiconv/)) can be installed on such
systems to remedy this deficiency, as well as on systems that do not supply
&[iconv()]& at all. After installing &%libiconv%&, you should add
.code
.vitem &%-bfp%&&~<&'prefix'&>
.oindex "&%-bfp%&"
+.cindex affix "filter testing"
This sets the prefix of the local part of the recipient address when a filter
file is being tested by means of the &%-bf%& option. The default is an empty
prefix.
.vitem &%-bfs%&&~<&'suffix'&>
.oindex "&%-bfs%&"
+.cindex affix "filter testing"
This sets the suffix of the local part of the recipient address when a filter
file is being tested by means of the &%-bf%& option. The default is an empty
suffix.
Features such as authentication and encryption, where the client input is not
plain text, cannot easily be tested with &%-bh%&. Instead, you should use a
specialized SMTP test program such as
-&url(http://jetmore.org/john/code/#swaks,swaks).
+&url(https://www.jetmore.org/john/code/swaks/,swaks).
.vitem &%-bhc%&&~<&'IP&~address'&>
.oindex "&%-bhc%&"
are available, similarly to the drivers. Because macros are sometimes used
for storing passwords, this option is restricted.
The output format is one item per line.
-.new
For the "-bP macro <name>" form, if no such macro is found
the exit status will be nonzero.
-.wen
.vitem &%-bp%&
.oindex "&%-bp%&"
&<<CHAPlocalscan>>&)
&`lookup `& general lookup code and all lookups
&`memory `& memory handling
-&`pid `& add pid to debug output lines
+&`noutf8 `& modifier: avoid UTF-8 line-drawing
+&`pid `& modifier: add pid to debug output lines
&`process_info `& setting info for the process log
&`queue_run `& queue runs
&`receive `& general message reception logic
&`retry `& retry handling
&`rewrite `& address rewriting
&`route `& address routing
-&`timestamp `& add timestamp to debug output lines
+&`timestamp `& modifier: add timestamp to debug output lines
&`tls `& TLS logic
&`transport `& transports
&`uid `& changes of uid/gid and looking up uid/gid
of all debug output lines. This can be useful when trying to track down delays
in processing.
+.new
+.cindex debugging "UTF-8 in"
+.cindex UTF-8 "in debug output"
+The &`noutf8`& selector disables the use of
+UTF-8 line-drawing characters to group related information.
+When disabled. ascii-art is used instead.
+Using the &`+all`& option does not set this modifier,
+.wen
+
If the &%debug_print%& option is set in any driver, it produces output whenever
any debugging is selected, or if &%-v%& is used.
only by an admin user or by the user who originally caused the message to be
placed on the queue.
+. .new
+. .vitem &%-MS%&
+. .oindex "&%-MS%&"
+. .cindex REQUIRETLS
+. This option is used to request REQUIRETLS processing on the message.
+. It is used internally by Exim in conjunction with -E when generating
+. a bounce message.
+. .wen
+
.vitem &%-Mset%&&~<&'message&~id'&>
-.oindex "&%-Mset%&
+.oindex "&%-Mset%&"
.cindex "testing" "string expansion"
.cindex "expansion" "testing"
This option is useful only in conjunction with &%-be%& (that is, when testing
&` _DRIVER_ROUTER_* `& router drivers
&` _DRIVER_TRANSPORT_* `& transport drivers
&` _DRIVER_AUTHENTICATOR_* `& authenticator drivers
+&` _LOG_* `& log_selector values
&` _OPT_MAIN_* `& main config options
&` _OPT_ROUTERS_* `& generic router options
&` _OPT_TRANSPORTS_* `& generic transport options
many Perl reference books, and also in
Jeffrey Friedl's &'Mastering Regular Expressions'&, which is published by
O'Reilly (see &url(http://www.oreilly.com/catalog/regex2/)).
+. --- the http: URL here redirects to another page with the ISBN in the URL
+. --- where trying to use https: just redirects back to http:, so sticking
+. --- to the old URL for now. 2018-09-07.
The documentation for the syntax and semantics of the regular expressions that
are supported by PCRE is included in the PCRE distribution, and no further
string without a terminating binary zero. The cdb format is designed for
indexed files that are read frequently and never updated, except by total
re-creation. As such, it is particularly suitable for large files containing
-aliases or other indexed data referenced by an MTA. Information about cdb can
-be found in several places:
+aliases or other indexed data referenced by an MTA. Information about cdb and
+tools for building the files can be found in several places:
.display
-&url(http://www.pobox.com/~djb/cdb.html)
-&url(ftp://ftp.corpit.ru/pub/tinycdb/)
-&url(http://packages.debian.org/stable/utils/freecdb.html)
+&url(https://cr.yp.to/cdb.html)
+&url(http://www.corpit.ru/mjt/tinycdb.html)
+&url(https://packages.debian.org/stable/utils/freecdb)
+&url(https://github.com/philpennock/cdbtools) (in Go)
.endd
+. --- 2018-09-07: corpit.ru http:-only
A cdb distribution is not needed in order to build Exim with cdb support,
because the code for reading cdb files is included directly in Exim itself.
However, no means of building or testing cdb files is provided with Exim, so
&*Warning*&: Unlike most other single-key lookup types, a file of data for
&((n)wildlsearch)& can &'not'& be turned into a DBM or cdb file, because those
lookup types support only literal keys.
+
+.next
+.cindex "lookup" "spf"
+If Exim is built with SPF support, manual lookups can be done
+(as opposed to the standard ACL condition method.
+For details see section &<<SECSPF>>&.
.endlist ilist
.next
.cindex "whoson lookup type"
.cindex "lookup" "whoson"
+. --- still http:-only, 2018-09-07
&(whoson)&: &'Whoson'& (&url(http://whoson.sourceforge.net)) is a protocol that
allows a server to check whether a particular (dynamically allocated) IP
address is currently allocated to a known (trusted) user and, optionally, to
${lookup redis{get keyname}}
.endd
-.new
As of release 4.91, "lightweight" support for Redis Cluster is available.
Requires &%redis_servers%& list to contain all the servers in the cluster, all
of which must be reachable from the running exim instance. If the cluster has
immediately follow the redirection but treats the response as a DEFER, moving on
to the next server in the &%redis_servers%& list until the correct server is
reached.
-.wen
.ecindex IIDfidalo1
.ecindex IIDfidalo2
If the ACL returns defer the result is a forced-fail. Otherwise the expansion fails.
-.new
.vitem "&*${authresults{*&<&'authserv-id'&>&*}}*&"
.cindex authentication "results header"
.cindex headers "authentication-results:"
add_header = :at_start:${authresults {$primary_hostname}}
.endd
This is safe even if no authentication results are available.
-.wen
.vitem "&*${certextract{*&<&'field'&>&*}{*&<&'certificate'&>&*}&&&
This forces an expansion failure (see section &<<SECTforexpfai>>&);
{<&'string2'&>} must be present for &"fail"& to be recognized.
+.new
+.vitem "&*${extract json{*&<&'key'&>&*}{*&<&'string1'&>&*}{*&<&'string2'&>&*}&&&
+ {*&<&'string3'&>&*}}*&"
+.cindex "expansion" "extracting from JSON object"
+.cindex JSON expansions
+The key and <&'string1'&> are first expanded separately. Leading and trailing
+white space is removed from the key (but not from any of the strings). The key
+must not be empty and must not consist entirely of digits.
+The expanded <&'string1'&> must be of the form:
+.display
+{ <&'"key1"'&> : <&'value1'&> , <&'"key2"'&> , <&'value2'&> ... }
+.endd
+.vindex "&$value$&"
+The braces, commas and colons, and the quoting of the member name are required;
+the spaces are optional.
+Matching of the key against the member names is done case-sensitively.
+. XXX should be a UTF-8 compare
+
+The results of matching are handled as above.
+.wen
+
.vitem "&*${extract{*&<&'number'&>&*}{*&<&'separators'&>&*}&&&
{*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*&"
empty (for example, the fifth field above).
+.new
+.vitem "&*${extract json{*&<&'number'&>&*}}&&&
+ {*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*&"
+.cindex "expansion" "extracting from JSON array"
+.cindex JSON expansions
+The <&'number'&> argument must consist entirely of decimal digits,
+apart from leading and trailing white space, which is ignored.
+
+Field selection and result handling is as above;
+there is no choice of field separator.
+.wen
+
+
.vitem &*${filter{*&<&'string'&>&*}{*&<&'condition'&>&*}}*&
.cindex "list" "selecting by condition"
.cindex "expansion" "selecting from list by condition"
&*$h_*&<&'header&~name'&>&*:*&" &&&
"&*$bheader_*&<&'header&~name'&>&*:*&&~or&~&&&
&*$bh_*&<&'header&~name'&>&*:*&" &&&
+ "&*$lheader_*&<&'header&~name'&>&*:*&&~or&~&&&
+ &*$lh_*&<&'header&~name'&>&*:*&"
"&*$rheader_*&<&'header&~name'&>&*:*&&~or&~&&&
&*$rh_*&<&'header&~name'&>&*:*&"
.cindex "expansion" "header insertion"
.vindex "&$header_$&"
.vindex "&$bheader_$&"
+.vindex "&$lheader_$&"
.vindex "&$rheader_$&"
.cindex "header lines" "in expansion strings"
.cindex "header lines" "character sets"
internal newlines (caused by splitting the header line over several physical
lines) may be present.
-The difference between &%rheader%&, &%bheader%&, and &%header%& is in the way
+The difference between the four pairs of expansions is in the way
the data in the header line is interpreted.
.ilist
&%rheader%& gives the original &"raw"& content of the header line, with no
processing at all, and without the removal of leading and trailing white space.
+.next
+.cindex "list" "of header lines"
+&%lheader%& gives a colon-separated list, one element per header when there
+are multiple headers with a given name.
+Any embedded colon characters within an element are doubled, so normal Exim
+list-processing facilities can be used.
+The terminating newline of each element is removed; in other respects
+the content is &"raw"&.
+
.next
.cindex "base64 encoding" "in header lines"
&%bheader%& removes leading and trailing white space, and then decodes base64
.code
${length_<n>:<string>}
.endd
-The result of this item is either the first <&'n'&> characters or the whole
+The result of this item is either the first <&'n'&> bytes or the whole
of <&'string2'&>, whichever is the shorter. Do not confuse &%length%& with
&%strlen%&, which gives the length of a string.
+All measurement is done in bytes and is not UTF-8 aware.
.vitem "&*${listextract{*&<&'number'&>&*}&&&
.code
${readsocket{/socket/name}{request string}{3s}}
.endd
+
The third argument is a list of options, of which the first element is the timeout
and must be present if the argument is given.
Further elements are options of form &'name=value'&.
-One option type is currently recognised, defining whether (the default)
+Two option types is currently recognised: shutdown and tls.
+The first defines whether (the default)
or not a shutdown is done on the connection after sending the request.
Example, to not do so (preferred, eg. by some webservers):
.code
${readsocket{/socket/name}{request string}{3s:shutdown=no}}
.endd
+.new
+The second, tls, controls the use of TLS on the connection. Example:
+.code
+${readsocket{/socket/name}{request string}{3s:tls=yes}}
+.endd
+The default is to not use TLS.
+If it is enabled, a shutdown as descripbed above is never done.
+.wen
+
A fourth argument allows you to change any newlines that are in the data
that is read, in the same way as for &%readfile%& (see above). This example
turns them into spaces:
.vitem &*$rheader_*&<&'header&~name'&>&*:*&&~or&~&*$rh_*&<&'header&~name'&>&*:*&
This item inserts &"raw"& header lines. It is described with the &%header%&
-expansion item above.
+expansion item in section &<<SECTexpansionitems>>& above.
.vitem "&*${run{*&<&'command'&>&*&~*&<&'args'&>&*}{*&<&'string1'&>&*}&&&
{*&<&'string2'&>&*}}*&"
yields &"K1=A K4=D K3=C"&. Note the use of &`\N`& to protect the contents of
the regular expression from string expansion.
+The regular expression is compiled in 8-bit mode, working against bytes
+rather than any Unicode-aware character handling.
.vitem &*${sort{*&<&'string'&>&*}{*&<&'comparator'&>&*}{*&<&'extractor'&>&*}}*&
If the starting offset is greater than the string length the result is the
null string; if the length plus starting offset is greater than the string
length, the result is the right-hand part of the string, starting from the
-given offset. The first character in the string has offset zero.
+given offset. The first byte (character) in the string has offset zero.
The &%substr%& expansion item can take negative offset values to count
-from the right-hand end of its operand. The last character is offset -1, the
-second-last is offset -2, and so on. Thus, for example,
+from the right-hand end of its operand. The last byte (character) is offset -1,
+the second-last is offset -2, and so on. Thus, for example,
.code
${substr{-5}{2}{1234567}}
.endd
yields &"1"&.
When the second number is omitted from &%substr%&, the remainder of the string
-is taken if the offset is positive. If it is negative, all characters in the
+is taken if the offset is positive. If it is negative, all bytes (characters) in the
string preceding the offset point are taken. For example, an offset of -1 and
no length, as in these semantically identical examples:
.code
.endd
yields all but the last character of the string, that is, &"abcd"&.
+All measurement is done in bytes and is not UTF-8 aware.
+
.vitem "&*${tr{*&<&'subject'&>&*}{*&<&'characters'&>&*}&&&
{*&<&'replacements'&>&*}}*&"
.cindex "expansion" "character translation"
.cindex "&%tr%& expansion item"
-This item does single-character translation on its subject string. The second
+This item does single-character (in bytes) translation on its subject string. The second
argument is a list of characters to be translated in the subject string. Each
matching character is replaced by the corresponding character from the
replacement list. For example
last occurrence is used. If the third string is shorter than the second, its
last character is replicated. However, if it is empty, no translation takes
place.
+
+All character handling is done in bytes and is not UTF-8 aware.
+
.endlist
header line, and the effective address is extracted from it. If the string does
not parse successfully, the result is empty.
+The parsing correctly handles SMTPUTF8 Unicode in the string.
+
.vitem &*${addresses:*&<&'string'&>&*}*&
.cindex "expansion" "RFC 2822 address handling"
example below is passed the contents of &`$header_from:`&, meaning it gets
de-mimed. Exim sees the decoded "," so it treats it as &*two*& email addresses.
The third example shows that the presence of a comma is skipped when it is
-quoted.
+quoted. The fourth example shows SMTPUTF8 handling.
.code
# exim -be '${addresses:From: \
=?iso-8859-2?Q?Last=2C_First?= <user@example.com>}'
Last:user@example.com
# exim -be '${addresses:From: "Last, First" <user@example.com>}'
user@example.com
+# exim -be '${addresses:フィル <フィリップ@example.jp>}'
+フィリップ@example.jp
.endd
.vitem &*${base32:*&<&'digits'&>&*}*&
.cindex "expansion" "hex to base64"
.cindex "&%hex2b64%& expansion item"
This operator converts a hex string into one that is base64 encoded. This can
-be useful for processing the output of the MD5 and SHA-1 hashing functions.
+be useful for processing the output of the various hashing functions.
.code
${lc:$local_part}
.endd
+Case is defined per the system C locale.
.vitem &*${length_*&<&'number'&>&*:*&<&'string'&>&*}*&
.cindex "expansion" "string truncation"
See the description of the general &%length%& item above for details. Note that
&%length%& is not the same as &%strlen%&. The abbreviation &%l%& can be used
when &%length%& is used as an operator.
+All measurement is done in bytes and is not UTF-8 aware.
.vitem &*${listcount:*&<&'string'&>&*}*&
The string is interpreted as an RFC 2822 address and the local part is
extracted from it. If the string does not parse successfully, the result is
empty.
+The parsing correctly handles SMTPUTF8 Unicode in the string.
.vitem &*${mask:*&<&'IP&~address'&>&*/*&<&'bit&~count'&>&*}*&
If you are creating a new email address from the contents of &$local_part$&
(or any other unknown data), you should always use this operator.
+This quoting determination is not SMTPUTF8-aware, thus quoting non-ASCII data
+will likely use the quoting form.
+Thus &'${quote_local_part:フィル}'& will always become &'"フィル"'&.
+
.vitem &*${quote_*&<&'lookup-type'&>&*:*&<&'string'&>&*}*&
.cindex "quoting" "lookup-specific"
The &%sha3%& expansion item is only supported if Exim has been
compiled with GnuTLS 3.5.0 or later,
-.new
or OpenSSL 1.1.1 or later.
The macro "_CRYPTO_HASH_SHA3" will be defined if it is supported.
-.wen
.vitem &*${stat:*&<&'string'&>&*}*&
.cindex "&%strlen%& expansion item"
The item is replace by the length of the expanded string, expressed as a
decimal number. &*Note*&: Do not confuse &%strlen%& with &%length%&.
+All measurement is done in bytes and is not UTF-8 aware.
.vitem &*${substr_*&<&'start'&>&*_*&<&'length'&>&*:*&<&'string'&>&*}*&
.endd
See the description of the general &%substr%& item above for details. The
abbreviation &%s%& can be used when &%substr%& is used as an operator.
+All measurement is done in bytes and is not UTF-8 aware.
.vitem &*${time_eval:*&<&'string'&>&*}*&
.cindex "&%time_eval%& expansion item"
.cindex "expansion" "case forcing"
.cindex "&%uc%& expansion item"
This forces the letters in the string into upper-case.
+Case is defined per the system C locale.
.vitem &*${utf8clean:*&<&'string'&>&*}*&
.cindex "correction of invalid utf-8 sequences in strings"
.cindex "expansion" "utf-8 forcing"
.cindex "&%utf8clean%& expansion item"
This replaces any invalid utf-8 sequence in the string by the character &`?`&.
+.new
+In versions of Exim before 4.92, this did not correctly do so for a truncated
+final codepoint's encoding, and the character would be silently dropped.
+If you must handle detection of this scenario across both sets of Exim behavior,
+the complexity will depend upon the task.
+For instance, to detect if the first character is multibyte and a 1-byte
+extraction can be successfully used as a path component (as is common for
+dividing up delivery folders), you might use:
+.code
+condition = ${if inlist{${utf8clean:${length_1:$local_part}}}{:?}{yes}{no}}
+.endd
+(which will false-positive if the first character of the local part is a
+literal question mark).
+.wen
.vitem "&*${utf8_domain_to_alabel:*&<&'string'&>&*}*&" &&&
"&*${utf8_domain_from_alabel:*&<&'string'&>&*}*&" &&&
.cindex "&%eqi%& expansion condition"
The two substrings are first expanded. The condition is true if the two
resulting strings are identical. For &%eq%& the comparison includes the case of
-letters, whereas for &%eqi%& the comparison is case-independent.
+letters, whereas for &%eqi%& the comparison is case-independent, where
+case is defined per the system C locale.
.vitem &*exists&~{*&<&'file&~name'&>&*}*&
.cindex "expansion" "file existence test"
string is lexically greater than or equal to the second string. For &%ge%& the
comparison includes the case of letters, whereas for &%gei%& the comparison is
case-independent.
+Case and collation order are defined per the system C locale.
.vitem &*gt&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& &&&
&*gti&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
string is lexically greater than the second string. For &%gt%& the comparison
includes the case of letters, whereas for &%gti%& the comparison is
case-independent.
+Case and collation order are defined per the system C locale.
.vitem &*inlist&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& &&&
&*inlisti&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
Both strings are expanded; the second string is treated as a list of simple
strings; if the first string is a member of the second, then the condition
is true.
+For the case-independent &%inlisti%& condition, case is defined per the system C locale.
These are simpler to use versions of the more powerful &*forany*& condition.
Examples, and the &*forany*& equivalents:
string is lexically less than or equal to the second string. For &%le%& the
comparison includes the case of letters, whereas for &%lei%& the comparison is
case-independent.
+Case and collation order are defined per the system C locale.
.vitem &*lt&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& &&&
&*lti&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
string is lexically less than the second string. For &%lt%& the comparison
includes the case of letters, whereas for &%lti%& the comparison is
case-independent.
+Case and collation order are defined per the system C locale.
.vitem &*match&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
and it may match anywhere in the subject, not just at the start. If you want
the pattern to match at the end of the subject, you must include the &`$`&
metacharacter at an appropriate point.
+All character handling is done in bytes and is not UTF-8 aware,
+but we might change this in a future Exim release.
.cindex "numerical variables (&$1$& &$2$& etc)" "in &%if%& expansion"
At the start of an &%if%& expansion the values of the numeric variable
.cindex "expansion" "PAM authentication test"
.cindex "&%pam%& expansion condition"
&'Pluggable Authentication Modules'&
-(&url(http://www.kernel.org/pub/linux/libs/pam/)) are a facility that is
+(&url(https://mirrors.edge.kernel.org/pub/linux/libs/pam/)) are a facility that is
available in the latest releases of Solaris and in some GNU/Linux
distributions. The Exim support, which is intended for use in conjunction with
the SMTP AUTH command, is available only if Exim is compiled with
In some operating systems, PAM authentication can be done only from a process
running as root. Since Exim is running as the Exim user when receiving
messages, this means that PAM cannot be used directly in those systems.
-A patched version of the &'pam_unix'& module that comes with the
-Linux PAM package is available from &url(http://www.e-admin.de/pam_exim/).
-The patched module allows one special uid/gid combination, in addition to root,
-to authenticate. If you build the patched module to allow the Exim user and
-group, PAM can then be used from an Exim authenticator.
+. --- 2018-09-07: the pam_exim modified variant has gone, removed claims re using Exim via that
.vitem &*pwcheck&~{*&<&'string1'&>&*:*&<&'string2'&>&*}*&
the value of &$authenticated_id$& is normally the login name of the calling
process. However, a trusted user can override this by means of the &%-oMai%&
command line option.
-.new
-This second case also sets up inforamtion used by the
+This second case also sets up information used by the
&$authresults$& expansion item.
-.wen
.vitem &$authenticated_fail_id$&
.cindex "authentication" "fail" "id"
inserting the message header line with the given name. Note that the name must
be terminated by colon or white space, because it may contain a wide variety of
characters. Note also that braces must &'not'& be used.
+See the full description in section &<<SECTexpansionitems>>& above.
.vitem &$headers_added$&
.vindex "&$headers_added$&"
the result, the name is not accepted, and &$host_lookup_deferred$& is set to
&"1"&. See also &$sender_host_name$&.
-.new
.cindex authentication "expansion item"
Performing these checks sets up information used by the
&$authresults$& expansion item.
-.wen
.vitem &$host_lookup_failed$&
.vindex "&$local_part_prefix$&"
.vindex "&$local_part_suffix$&"
+.cindex affix variables
If a local part prefix or suffix has been recognized, it is not included in the
value of &$local_part$& during routing and subsequent delivery. The values of
any prefix or suffix are in &$local_part_prefix$& and
.vitem &$local_part_prefix$&
.vindex "&$local_part_prefix$&"
+.cindex affix variables
When an address is being routed or delivered, and a
specific prefix for the local part was recognized, it is available in this
variable, having been removed from &$local_part$&.
is compiled with the content-scanning extension. For details, see section
&<<SECTscanspamass>>&.
-.new
.vitem &$spf_header_comment$& &&&
&$spf_received$& &&&
&$spf_result$& &&&
&$spf_smtp_comment$&
These variables are only available if Exim is built with SPF support.
For details see section &<<SECSPF>>&.
-.wen
.vitem &$spool_directory$&
.vindex "&$spool_directory$&"
.row &%av_scanner%& "specify virus scanner"
.row &%check_rfc2047_length%& "check length of RFC 2047 &""encoded &&&
words""&"
+.row &%dns_cname_loops%& "follow CNAMEs returned by resolver"
.row &%dns_csa_search_limit%& "control CSA parent search depth"
.row &%dns_csa_use_reverse%& "en/disable CSA IP reverse search"
.row &%header_maxsize%& "total size of message header"
It now defaults to true.
A more detailed analysis of the issues is provided by Dan Bernstein:
.display
-&url(http://cr.yp.to/smtp/8bitmime.html)
+&url(https://cr.yp.to/smtp/8bitmime.html)
.endd
To log received 8BITMIME status use
reversed and looked up in the reverse DNS, as described in more detail in
section &<<SECTverifyCSA>>&.
+.new
+.option dns_cname_loops main integer 1
+.cindex DNS "CNAME following"
+This option controls the following of CNAME chains, needed if the resolver does
+not do it internally.
+As of 2018 most should, and the default can be left.
+If you have an ancient one, a value of 10 is likely needed.
+
+The default value of one CNAME-follow is needed
+thanks to the observed return for an MX request,
+given no MX presence but a CNAME to an A, of the CNAME.
+.wen
+
.option dns_dnssec_ok main integer -1
.cindex "DNS" "resolver options"
implementations of TLS.
-option gnutls_allow_auto_pkcs11 main boolean unset
+.option gnutls_allow_auto_pkcs11 main boolean unset
This option will let GnuTLS (2.12.0 or later) autoload PKCS11 modules with
the p11-kit configuration files in &_/etc/pkcs11/modules/_&.
See
-&url(http://www.gnutls.org/manual/gnutls.html#Smart-cards-and-HSMs)
+&url(https://www.gnutls.org/manual/gnutls.html#Smart-cards-and-HSMs)
for documentation.
-.new
.option spf_guess main string "v=spf1 a/24 mx/24 ptr ?all"
This option is available when Exim is compiled with SPF support.
See section &<<SECSPF>>& for more details.
-.wen
This option specifies a certificate revocation list. The expanded value must
be the name of a file that contains CRLs in PEM format.
-.new
Under OpenSSL the option can specify a directory with CRL files.
&*Note:*& Under OpenSSL the option must, if given, supply a CRL
for each signing element of the certificate chain (i.e. all but the leaf).
For the file variant this can be multiple PEM blocks in the one file.
-.wen
See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
Usable for GnuTLS 3.4.4 or 3.3.17 or OpenSSL 1.1.0 (or later).
-.new
For GnuTLS 3.5.6 or later the expanded value of this option can be a list
of files, to match a list given for the &%tls_certificate%& option.
The ordering of the two lists must match.
-.wen
.option tls_on_connect_ports main "string list" unset
.cindex SSMTP
.cindex SMTPS
This option specifies a list of incoming SSMTP (aka SMTPS) ports that should
-operate the obsolete SSMTP (SMTPS) protocol, where a TLS session is immediately
+operate the SSMTP (SMTPS) protocol, where a TLS session is immediately
set up without waiting for the client to issue a STARTTLS command. For
further details, see section &<<SECTsupobssmt>>&.
.option local_part_prefix routers&!? "string list" unset
+.cindex affix "router precondition"
.cindex "router" "prefix for local part"
.cindex "prefix" "for local part, used in router"
If this option is set, the router is skipped unless the local part starts with
MX records of equal priority are sorted by Exim into a random order. Exim then
looks for address records for the host names obtained from MX or SRV records.
When a host has more than one IP address, they are sorted into a random order,
-.new
except that IPv6 addresses are sorted before IPv4 addresses. If all the
-.wen
IP addresses found are discarded by a setting of the &%ignore_target_hosts%&
generic option, the router declines.
also being queued.
-.new
.option ipv4_only "string&!!" unset
.cindex IPv6 disabling
.cindex DNS "IPv6 disabling"
or an empty string, or one of the strings “0” or “no” or “false”
(checked without regard to the case of the letters),
A records are sorted before AAAA records (inverting the default).
-.wen
.option mx_domains dnslookup "domain list&!!" unset
.cindex "MX record" "required to exist"
A list of hosts, whether obtained via &%route_data%& or &%route_list%&, is
always separately expanded before use. If the expansion fails, the router
declines. The result of the expansion must be a colon-separated list of names
-and/or IP addresses, optionally also including ports. The format of each item
+and/or IP addresses, optionally also including ports.
+If the list is written with spaces, it must be protected with quotes.
+The format of each item
in the list is described in the next section. The list separator can be changed
as described in section &<<SECTlistconstruct>>&.
&%bydns%&: look up address records for the hosts directly in the DNS; fail if
no address records are found. If there is a temporary DNS error (such as a
timeout), delivery is deferred.
-.new
.next
&%ipv4_only%&: in direct DNS lookups, look up only A records.
.next
&%ipv4_prefer%&: in direct DNS lookups, sort A records before AAAA records.
-.wen
.endlist
For example:
option.
-.new
.option dane_require_tls_ciphers smtp string&!! unset
.cindex "TLS" "requiring specific ciphers for DANE"
.cindex "cipher" "requiring specific"
counter-intuitively decreasing it.
If the option expands to be empty or is forced to fail, then it will
be treated as unset and &%tls_require_ciphers%& will be used instead.
-.wen
.option data_timeout smtp time 5m
of the message. Its value must not be zero. See also &%final_timeout%&.
+.option dkim_canon smtp string&!! unset
.option dkim_domain smtp string list&!! unset
-.option dkim_selector smtp string&!! unset
+.option dkim_hash smtp string&!! sha256
+.option dkim_identity smtp string&!! unset
.option dkim_private_key smtp string&!! unset
-.option dkim_canon smtp string&!! unset
+.option dkim_selector smtp string&!! unset
.option dkim_strict smtp string&!! unset
.option dkim_sign_headers smtp string&!! "per RFC"
-.option dkim_hash smtp string&!! sha256
-.option dkim_identity smtp string&!! unset
+.option dkim_timestamps smtp string&!! unset
DKIM signing options. For details see section &<<SECDKIMSIGN>>&.
.option delay_after_cutoff smtp boolean true
+.cindex "final cutoff" "retries, controlling"
+.cindex retry "final cutoff"
This option controls what happens when all remote IP addresses for a given
domain have been inaccessible for so long that they have passed their retry
cutoff times.
TLS session for any host that matches this list.
&%tls_verify_certificates%& should also be set for the transport.
-.new
.option hosts_require_dane smtp "host list&!!" unset
.cindex DANE "transport options"
.cindex DANE "requiring for certain servers"
and that a DANE-verified TLS connection is made.
There will be no fallback to in-clear communication.
See section &<<SECDANE>>&.
-.wen
.option hosts_require_ocsp smtp "host list&!!" unset
.cindex "TLS" "requiring for certain servers"
CHUNKING support, Exim will attempt to use BDAT commands rather than DATA.
BDAT will not be used in conjunction with a transport filter.
-.new
.option hosts_try_dane smtp "host list&!!" unset
.cindex DANE "transport options"
.cindex DANE "attempting for certain servers"
a DANE-verified TLS connection is made to that host;
there will be no fallback to in-clear communication.
See section &<<SECDANE>>&.
-.wen
.option hosts_try_fastopen smtp "host list&!!" unset
.cindex "fast open, TCP" "enabling, in client"
If the value of this option begins with a digit it is taken as a port number;
otherwise it is looked up using &[getservbyname()]&. The default value is
-normally &"smtp"&, but if &%protocol%& is set to &"lmtp"&, the default is
-&"lmtp"&. If the expansion fails, or if a port number cannot be found, delivery
+normally &"smtp"&,
+but if &%protocol%& is set to &"lmtp"& the default is &"lmtp"&
+and if &%protocol%& is set to &"smtps"& the default is &"smtps"&.
+If the expansion fails, or if a port number cannot be found, delivery
is deferred.
+.new
+Note that at least one Linux distribution has been seen failing
+to put &"smtps"& in its &"/etc/services"& file, resulting is such deferrals.
+.wen
+
.option protocol smtp string smtp
If this option is set to &"smtps"&, the default value for the &%port%& option
changes to &"smtps"&, and the transport initiates TLS immediately after
connecting, as an outbound SSL-on-connect, instead of using STARTTLS to upgrade.
-The Internet standards bodies strongly discourage use of this mode.
+.new
+The Internet standards bodies used to strongly discourage use of this mode,
+but as of RFC 8314 it is perferred over STARTTLS for message submission
+(as distinct from MTA-MTA communication).
+.wen
.option retry_include_ip_address smtp boolean&!! true
If both this option and &%tls_try_verify_hosts%& are unset
operation is as if this option selected all hosts.
+.new
+.option utf8_downconvert smtp integer!! unset
+.cindex utf8 "address downconversion"
+.cindex i18n "utf8 address downconversion"
+If built with internationalization support,
+this option controls conversion of UTF-8 in message addresses
+to a-label form.
+For details see section &<<SECTi18nMTA>>&.
+.wen
+
messages. If this delivery fails, the address fails immediately. The
post-cutoff retry time is not used.
+.cindex "final cutoff" "retries, controlling"
+.cindex retry "final cutoff"
If the delivery is remote, there are two possibilities, controlled by the
.oindex "&%delay_after_cutoff%&"
&%delay_after_cutoff%& option of the &(smtp)& transport. The option is true by
-default. Until the post-cutoff retry time for one of the IP addresses is
+default. Until the post-cutoff retry time for one of the IP addresses,
+as set by the &%retry_data_expire%& option, is
reached, the failing email address is bounced immediately, without a delivery
attempt taking place. After that time, one new delivery attempt is made to
those IP addresses that are past their retry times, and if that still fails,
AUTH_CRAM_MD5=yes
AUTH_CYRUS_SASL=yes
AUTH_DOVECOT=yes
+AUTH_EXTERNAL=yes
AUTH_GSASL=yes
AUTH_HEIMDAL_GSSAPI=yes
AUTH_PLAINTEXT=yes
the Cyrus SASL authentication library.
The third is an interface to Dovecot's authentication system, delegating the
work via a socket interface.
-The fourth provides an interface to the GNU SASL authentication library, which
+.new
+The fourth provides for negotiation of authentication done via non-SMTP means,
+as defined by RFC 4422 Appendix A.
+.wen
+The fifth provides an interface to the GNU SASL authentication library, which
provides mechanisms but typically not data sources.
-The fifth provides direct access to Heimdal GSSAPI, geared for Kerberos, but
+The sixth provides direct access to Heimdal GSSAPI, geared for Kerberos, but
supporting setting a server keytab.
-The sixth can be configured to support
+The seventh can be configured to support
the PLAIN authentication mechanism (RFC 2595) or the LOGIN mechanism, which is
-not formally documented, but used by several MUAs. The seventh authenticator
+not formally documented, but used by several MUAs.
+The eighth authenticator
supports Microsoft's &'Secure Password Authentication'& mechanism.
-The eighth is an Exim authenticator but not an SMTP one;
+The last is an Exim authenticator but not an SMTP one;
instead it can use information from a TLS negotiation.
The authenticators are configured using the same syntax as other drivers (see
.option server_set_id authenticators string&!! unset
.vindex "&$authenticated_id$&"
+.vindex "&$authenticated_fail_id$&"
When an Exim server successfully authenticates a client, this string is
expanded using data from the authentication, and preserved for any incoming
messages in the variable &$authenticated_id$&. It is also included in the log
lines for incoming messages. For example, a user/password authenticator
configuration might preserve the user name that was used to authenticate, and
refer to it subsequently during delivery of the message.
+On a failing authentication the expansion result is instead saved in
+the &$authenticated_fail_id$& variable.
If expansion fails, the option is ignored.
client from which the message was received. This variable is empty if there was
no successful authentication.
-.new
.cindex authentication "expansion item"
Successful authentication sets up information used by the
&$authresults$& expansion item.
-.wen
expansion is &"1"&, &"yes"&, or &"true"&, authentication succeeds and the
generic &%server_set_id%& option is expanded and saved in &$authenticated_id$&.
For any other result, a temporary error code is returned, with the expanded
-string as the error text
+string as the error text.
&*Warning*&: If you use a lookup in the expansion to find the user's
password, be sure to make the authentication fail if the user is unknown.
.scindex IIDcyrauth2 "authenticators" "&(cyrus_sasl)&"
.cindex "Cyrus" "SASL library"
.cindex "Kerberos"
-The code for this authenticator was provided by Matthew Byng-Maddick of A L
-Digital Ltd (&url(http://www.aldigital.co.uk)).
+The code for this authenticator was provided by Matthew Byng-Maddick while
+at A L Digital Ltd.
The &(cyrus_sasl)& authenticator provides server support for the Cyrus SASL
library implementation of the RFC 2222 (&"Simple Authentication and Security
.option server_socket dovecot string unset
-This option must specify the socket that is the interface to Dovecot
+This option must specify the UNIX socket that is the interface to Dovecot
authentication. The &%public_name%& option must specify an authentication
mechanism that Dovecot is configured to support. You can have several
authenticators for different mechanisms. For example:
.option server_channelbinding gsasl boolean false
+Do not set this true without consulting a cryptographic engineer.
+
Some authentication mechanisms are able to use external context at both ends
of the session to bind the authentication to that context, and fail the
authentication process if that context differs. Specifically, some TLS
ciphersuites can provide identifying information about the cryptographic
context.
-This means that certificate identity and verification becomes a non-issue,
-as a man-in-the-middle attack will cause the correct client and server to
-see different identifiers and authentication will fail.
+This should have meant that certificate identity and verification becomes a
+non-issue, as a man-in-the-middle attack will cause the correct client and
+server to see different identifiers and authentication will fail.
This is currently only supported when using the GnuTLS library. This is
only usable by mechanisms which support "channel binding"; at time of
This defaults off to ensure smooth upgrade across Exim releases, in case
this option causes some clients to start failing. Some future release
-of Exim may switch the default to be true.
+of Exim might have switched the default to be true.
+
+However, Channel Binding in TLS has proven to be broken in current versions.
+Do not plan to rely upon this feature for security, ever, without consulting
+with a subject matter expert (a cryptographic engineer).
.option server_hostname gsasl string&!! "see below"
Password Authentication'& mechanism,
which is also sometimes known as NTLM (NT LanMan). The code for client side of
this authenticator was contributed by Marc Prud'hommeaux, and much of it is
-taken from the Samba project (&url(http://www.samba.org)). The code for the
+taken from the Samba project (&url(https://www.samba.org/)). The code for the
server side was subsequently contributed by Tom Kistner. The mechanism works as
follows:
+. ////////////////////////////////////////////////////////////////////////////
+. ////////////////////////////////////////////////////////////////////////////
+
+.chapter "The external authenticator" "CHAPexternauth"
+.scindex IIDexternauth1 "&(external)& authenticator"
+.scindex IIDexternauth2 "authenticators" "&(external)&"
+.cindex "authentication" "Client Certificate"
+.cindex "authentication" "X509"
+.cindex "Certificate-based authentication"
+The &(external)& authenticator provides support for
+authentication based on non-SMTP information.
+The specification is in RFC 4422 Appendix A
+(&url(https://tools.ietf.org/html/rfc4422)).
+It is only a transport and negotiation mechanism;
+the process of authentication is entirely controlled
+by the server configuration.
+
+The client presents an identity in-clear.
+It is probably wise for a server to only advertise,
+and for clients to only attempt,
+this authentication method on a secure (eg. under TLS) connection.
+
+One possible use, compatible with the
+K-9 Mail Andoid client (&url(https://k9mail.github.io/)),
+is for using X509 client certificates.
+
+It thus overlaps in function with the TLS authenticator
+(see &<<CHAPtlsauth>>&)
+but is a full SMTP SASL authenticator
+rather than being implicit for TLS-connection carried
+client certificates only.
+
+The examples and discussion in this chapter assume that
+client-certificate authentication is being done.
+
+The client must present a certificate,
+for which it must have been requested via the
+&%tls_verify_hosts%& or &%tls_try_verify_hosts%& main options
+(see &<<CHAPTLS>>&).
+For authentication to be effective the certificate should be
+verifiable against a trust-anchor certificate known to the server.
+
+.section "External options" "SECTexternsoptions"
+.cindex "options" "&(external)& authenticator (server)"
+The &(external)& authenticator has two server options:
+
+.option server_param2 external string&!! unset
+.option server_param3 external string&!! unset
+.cindex "variables (&$auth1$& &$auth2$& etc)" "in &(external)& authenticator"
+These options are expanded before the &%server_condition%& option
+and the result are placed in &$auth2$& and &$auth3$& resectively.
+If the expansion is forced to fail, authentication fails. Any other expansion
+failure causes a temporary error code to be returned.
+
+They can be used to clarify the coding of a complex &%server_condition%&.
+
+.section "Using external in a server" "SECTexternserver"
+.cindex "AUTH" "in &(external)& authenticator"
+.cindex "numerical variables (&$1$& &$2$& etc)" &&&
+ "in &(external)& authenticator"
+.vindex "&$auth1$&, &$auth2$&, etc"
+.cindex "base64 encoding" "in &(external)& authenticator"
+
+When running as a server, &(external)& performs the authentication test by
+expanding a string. The data sent by the client with the AUTH command, or in
+response to subsequent prompts, is base64 encoded, and so may contain any byte
+values when decoded. The decoded value is treated as
+an identity for authentication and
+placed in the expansion variable &$auth1$&.
+
+For compatibility with previous releases of Exim, the value is also placed in
+the expansion variable &$1$&. However, the use of this
+variable for this purpose is now deprecated, as it can lead to confusion in
+string expansions that also use them for other things.
+
+.vindex "&$authenticated_id$&"
+Once an identity has been received,
+&%server_condition%& is expanded. If the expansion is forced to fail,
+authentication fails. Any other expansion failure causes a temporary error code
+to be returned. If the result of a successful expansion is an empty string,
+&"0"&, &"no"&, or &"false"&, authentication fails. If the result of the
+expansion is &"1"&, &"yes"&, or &"true"&, authentication succeeds and the
+generic &%server_set_id%& option is expanded and saved in &$authenticated_id$&.
+For any other result, a temporary error code is returned, with the expanded
+string as the error text.
+
+Example:
+.code
+ext_ccert_san_mail:
+ driver = external
+ public_name = EXTERNAL
+
+ server_advertise_condition = $tls_in_certificate_verified
+ server_param2 = ${certextract {subj_altname,mail,>:} \
+ {$tls_in_peercert}}
+ server_condition = ${if forany {$auth2} \
+ {eq {$item}{$auth1}}}
+ server_set_id = $auth1
+.endd
+This accepts a client certificate that is verifiable against any
+of your configured trust-anchors
+(which usually means the full set of public CAs)
+and which has a mail-SAN matching the claimed identity sent by the client.
+
+Note that, up to TLS1.2, the client cert is on the wire in-clear, including the SAN,
+The account name is therefore guessable by an opponent.
+TLS 1.3 protects both server and client certificates, and is not vulnerable
+in this way.
+Likewise, a traditional plaintext SMTP AUTH done inside TLS is not.
+
+
+.section "Using external in a client" "SECTexternclient"
+.cindex "options" "&(external)& authenticator (client)"
+The &(external)& authenticator has one client option:
+
+.option client_send external string&!! unset
+This option is expanded and sent with the AUTH command as the
+identity being asserted.
+
+Example:
+.code
+ext_ccert:
+ driver = external
+ public_name = EXTERNAL
+
+ client_condition = ${if !eq{$tls_out_cipher}{}}
+ client_send = myaccount@smarthost.example.net
+.endd
+
+
+.ecindex IIDexternauth1
+.ecindex IIDexternauth2
+
+
+
+
+
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
driver = tls
server_param1 = ${certextract {subj_altname,mail,>:} \
{$tls_in_peercert}}
- server_condition = ${if forany {$auth1} \
+ server_condition = ${if and { {eq{$tls_in_certificate_verified}{1}} \
+ {forany {$auth1} \
{!= {0} \
{${lookup ldap{ldap:///\
mailname=${quote_ldap_dn:${lc:$item}},\
ou=users,LDAP_DC?mailid} {$value}{0} \
- } } } }
+ } } } }}}
server_set_id = ${if = {1}{${listcount:$auth1}} {$auth1}{}}
.endd
This accepts a client certificate that is verifiable against any
of your configured trust-anchors
(which usually means the full set of public CAs)
and which has a SAN with a good account name.
-Note that the client cert is on the wire in-clear, including the SAN,
-whereas a plaintext SMTP AUTH done inside TLS is not.
+
+Note that, up to TLS1.2, the client cert is on the wire in-clear, including the SAN,
+The account name is therefore guessable by an opponent.
+TLS 1.3 protects both server and client certificates, and is not vulnerable
+in this way.
+Likewise, a traditional plaintext SMTP AUTH done inside TLS is not.
. An alternative might use
. .code
.oindex "&%tls_require_ciphers%&" "OpenSSL"
There is a function in the OpenSSL library that can be passed a list of cipher
suites before the cipher negotiation takes place. This specifies which ciphers
-are acceptable. The list is colon separated and may contain names like
+.new
+are acceptable for TLS versions prior to 1.3.
+.wen
+The list is colon separated and may contain names like
DES-CBC3-SHA. Exim passes the expanded value of &%tls_require_ciphers%&
directly to this function call.
Many systems will install the OpenSSL manual-pages, so you may have
tls_require_ciphers = ECDSA:RSA:!COMPLEMENTOFDEFAULT
.endd
+.new
+For TLS version 1.3 the control available is less fine-grained
+and Exim does not provide access to it at present.
+The value of the &%tls_require_ciphers%& option is ignored when
+TLS version 1.3 is negotiated.
+
+As of writing the library default cipher suite list for TLSv1.3 is
+.code
+TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256
+.endd
+.wen
+
.section "Requiring specific ciphers or other parameters in GnuTLS" &&&
"SECTreqciphgnu"
Documentation of the strings accepted may be found in the GnuTLS manual, under
"Priority strings". This is online as
-&url(http://www.gnutls.org/manual/html_node/Priority-Strings.html),
+&url(https://www.gnutls.org/manual/html_node/Priority-Strings.html),
but beware that this relates to GnuTLS 3, which may be newer than the version
installed on your system. If you are using GnuTLS 3,
then the example code
-&url(http://www.gnutls.org/manual/gnutls.html#Listing-the-ciphersuites-in-a-priority-string)
+&url(https://www.gnutls.org/manual/gnutls.html#Listing-the-ciphersuites-in-a-priority-string)
on that site can be used to test a given string.
For example:
apply to all TLS connections. For any host that matches one of these options,
Exim requests a certificate as part of the setup of the TLS session. The
contents of the certificate are verified by comparing it with a list of
-expected certificates.
+expected trust-anchors or certificates.
These may be the system default set (depending on library version),
an explicit file or,
depending on library version, a directory, identified by
.endd
where &_/cert/file_& contains a single certificate.
+There is no checking of names of the client against the certificate
+Subject Name or Subject Alternate Names.
+
The difference between &%tls_verify_hosts%& and &%tls_try_verify_hosts%& is
what happens if the client does not supply a certificate, or if the certificate
does not match any of the certificates in the collection named by
certificate verification to the listed servers. Verification either must
or need not succeed respectively.
+The &%tls_verify_cert_hostnames%& option lists hosts for which additional
+checks are made: that the host name (the one in the DNS A record)
+is valid for the certificate.
+The option defaults to always checking.
+
The &(smtp)& transport has two OCSP-related options:
&%hosts_require_ocsp%&; a host-list for which a Certificate Status
is requested and required for the connection to proceed. The default
.section "Certificates and all that" "SECTcerandall"
.cindex "certificate" "references to discussion"
In order to understand fully how TLS works, you need to know about
-certificates, certificate signing, and certificate authorities. This is not the
-place to give a tutorial, especially as I do not know very much about it
-myself. Some helpful introduction can be found in the FAQ for the SSL addition
-to Apache, currently at
+certificates, certificate signing, and certificate authorities.
+This is a large topic and an introductory guide is unsuitable for the Exim
+reference manual, so instead we provide pointers to existing documentation.
+
+The Apache web-server was for a long time the canonical guide, so their
+documentation is a good place to start; their SSL module's Introduction
+document is currently at
.display
-&url(http://www.modssl.org/docs/2.7/ssl_faq.html#ToC24)
+&url(https://httpd.apache.org/docs/current/ssl/ssl_intro.html)
.endd
-Other parts of the &'modssl'& documentation are also helpful, and have
-links to further files.
-Eric Rescorla's book, &'SSL and TLS'&, published by Addison-Wesley (ISBN
-0-201-61598-3), contains both introductory and more in-depth descriptions.
-Some sample programs taken from the book are available from
+and their FAQ is at
.display
-&url(http://www.rtfm.com/openssl-examples/)
+&url(https://httpd.apache.org/docs/current/ssl/ssl_faq.html)
.endd
+Eric Rescorla's book, &'SSL and TLS'&, published by Addison-Wesley (ISBN
+0-201-61598-3) in 2001, contains both introductory and more in-depth
+descriptions.
+More recently Ivan Ristić's book &'Bulletproof SSL and TLS'&,
+published by Feisty Duck (ISBN 978-1907117046) in 2013 is good.
+Ivan is the author of the popular TLS testing tools at
+&url(https://www.ssllabs.com/).
+
.section "Certificate chains" "SECID186"
The file named by &%tls_certificate%& may contain more than one
For information on creating self-signed CA certificates and using them to sign
user certificates, see the &'General implementation overview'& chapter of the
Open-source PKI book, available online at
-&url(http://ospkibook.sourceforge.net/).
+&url(https://sourceforge.net/projects/ospkibook/).
.ecindex IIDencsmtp1
.ecindex IIDencsmtp2
-.new
.section DANE "SECDANE"
.cindex DANE
DNS-based Authentication of Named Entities, as applied to SMTP over TLS, provides assurance to a client that
in &_Local/Makefile_&.
If it has been included, the macro "_HAVE_DANE" will be defined.
-The TLSA record for the server may have "certificate usage" of DANE-TA(2) or DANE-EE(3). The latter specifies
-the End Entity directly, i.e. the certificate involved is that of the server (and should be the sole one transmitted
-during the TLS handshake); this is appropriate for a single system, using a self-signed certificate.
+The TLSA record for the server may have "certificate usage" of DANE-TA(2) or DANE-EE(3).
+These are the "Trust Anchor" and "End Entity" variants.
+The latter specifies the End Entity directly, i.e. the certificate involved is that of the server
+(and if only DANE-EE is used then it should be the sole one transmitted during the TLS handshake);
+this is appropriate for a single system, using a self-signed certificate.
DANE-TA usage is effectively declaring a specific CA to be used; this might be a private CA or a public,
-well-known one. A private CA at simplest is just a self-signed certificate which is used to sign
-cerver certificates, but running one securely does require careful arrangement. If a private CA is used
-then either all clients must be primed with it, or (probably simpler) the server TLS handshake must transmit
-the entire certificate chain from CA to server-certificate. If a public CA is used then all clients must be primed with it
-(losing one advantage of DANE) - but the attack surface is reduced from all public CAs to that single CA.
+well-known one.
+A private CA at simplest is just a self-signed certificate (with certain
+attributes) which is used to sign server certificates, but running one securely
+does require careful arrangement.
+With DANE-TA, as implemented in Exim and commonly in other MTAs,
+the server TLS handshake must transmit the entire certificate chain from CA to server-certificate.
DANE-TA is commonly used for several services and/or servers, each having a TLSA query-domain CNAME record,
all of which point to a single TLSA record.
+DANE-TA and DANE-EE can both be used together.
-Another approach which should be seriously considered is to use DANE with a certificate
-from a public CA, because of another technology, "MTA-STS", described below.
+.new
+Our recommendation is to use DANE with a certificate from a public CA,
+because this enables a variety of strategies for remote clients to verify
+your certificate.
+You can then publish information both via DANE and another technology,
+"MTA-STS", described below.
+
+When you use DANE-TA to publish trust anchor information, you ask entities
+outside your administrative control to trust the Certificate Authority for
+connections to you.
+If using a private CA then you should expect others to still apply the
+technical criteria they'd use for a public CA to your certificates.
+In particular, you should probably try to follow current best practices for CA
+operation around hash algorithms and key sizes.
+Do not expect other organizations to lower their security expectations just
+because a particular profile might be reasonable for your own internal use.
+
+When this text was last updated, this in practice means to avoid use of SHA-1
+and MD5; if using RSA to use key sizes of at least 2048 bits (and no larger
+than 4096, for interoperability); to use keyUsage fields correctly; to use
+random serial numbers.
+The list of requirements is subject to change as best practices evolve.
+If you're not already using a private CA, or it doesn't meet these
+requirements, then we encourage you to avoid all these issues and use a public
+CA such as &url(https://letsencrypt.org/,Let's Encrypt) instead.
+.wen
The TLSA record should have a Selector field of SPKI(1) and a Matching Type field of SHA2-512(2).
For use with the DANE-TA model, server certificates must have a correct name (SubjectName or SubjectAltName).
+.new
+The Certificate issued by the CA published in the DANE-TA model should be
+issued using a strong hash algorithm.
+Exim, and importantly various other MTAs sending to you, will not
+re-enable hash algorithms which have been disabled by default in TLS
+libraries.
+This means no MD5 and no SHA-1. SHA2-256 is the minimum for reliable
+interoperability (and probably the maximum too, in 2018).
+.wen
+
The use of OCSP-stapling should be considered, allowing for fast revocation of certificates (which would otherwise
be limited by the DNS TTL on the TLSA records). However, this is likely to only be usable with DANE-TA. NOTE: the
default of requesting OCSP for all hosts is modified iff DANE is in use, to:
information.
The MTA-STS design requires a certificate from a public Certificate Authority
-which is recognized by clients sending to you. That selection is outside your
-control.
+which is recognized by clients sending to you.
+That selection of which CAs are trusted by others is outside your control.
The most interoperable course of action is probably to use
&url(https://letsencrypt.org/,Let's Encrypt), with automated certificate
information for MTA-STS as well. This is what is done for the &'exim.org'&
domain itself (with caveats around occasionally broken MTA-STS because of
incompatible specification changes prior to reaching RFC status).
-.wen
warn message = Remove internal headers
remove_header = $acl_c_ihdrs
.endd
-Removed header lines are accumulated during the MAIL, RCPT, and predata ACLs.
-They are removed from the message before processing the DATA and MIME ACLs.
-There is no harm in attempting to remove the same header twice nor is removing
+Header names for removal are accumulated during the MAIL, RCPT, and predata ACLs.
+Matching header lines are removed from the message before processing the DATA and MIME ACLs.
+If multiple header lines match, all are removed.
+There is no harm in attempting to remove the same header twice nor in removing
a non-existent header. Further header lines to be removed may be accumulated
during the DATA and MIME ACLs, after which they are removed from the message,
if present. In the case of non-SMTP messages, headers to be removed are
Exim does not share information between multiple incoming
connections (but your local name server cache should be active).
+There are a number of DNS lists to choose from, some commercial, some free,
+or free for small deployments. An overview can be found at
+&url(https://en.wikipedia.org/wiki/Comparison_of_DNS_blacklists).
+
.section "Specifying the IP address for a DNS list lookup" "SECID201"
.section "DNS lists keyed on domain names" "SECID202"
.cindex "DNS list" "keyed by domain name"
There are some lists that are keyed on domain names rather than inverted IP
-addresses (see for example the &'domain based zones'& link at
-&url(http://www.rfc-ignorant.org/)). No reversing of components is used
+addresses. No reversing of components is used
with these lists. You can change the name that is looked up in a DNS list by
listing it after the domain name, introduced by a slash. For example,
.code
a check that the IP being tested is indeed on the first list. The first
domain is the one that is put in &$dnslist_domain$&. For example:
.code
-reject message = \
+deny message = \
rejected because $sender_host_address is blacklisted \
at $dnslist_domain\n$dnslist_text
dnslists = \
given several times, but because the results of the DNS lookups are cached,
the DNS calls themselves are not repeated. For example:
.code
-reject dnslists = \
+deny dnslists = \
http.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.2 : \
socks.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.3 : \
misc.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.4 : \
The &%leaky%& (default) option means that the client's recorded rate is not
updated if it is above the limit. The effect of this is that Exim measures the
-client's average rate of successfully sent email, which cannot be greater than
-the maximum allowed. If the client is over the limit it may suffer some
-counter-measures (as specified in the ACL), but it will still be able to send
-email at the configured maximum rate, whatever the rate of its attempts. This
+client's average rate of successfully sent email,
+.new
+up to the given limit.
+This is appropriate if the countermeasure when the condition is true
+consists of refusing the message, and
is generally the better choice if you have clients that retry automatically.
-For example, it does not prevent a sender with an over-aggressive retry rate
-from getting any email through.
+If the action when true is anything more complex then this option is
+likely not what is wanted.
+.wen
The &%strict%& option means that the client's recorded rate is always
updated. The effect of this is that Exim measures the client's average rate
The main use of these variables is expected to be to distinguish between
rejections of MAIL and rejections of RCPT in callouts.
+.new
+The above variables may also be set after a &*successful*&
+address verification to:
+
+.ilist
+&%random%&: A random local-part callout succeeded
+.endlist
+.wen
+
Exim's side of the malware scanner, or are given on separate lines to
the daemon as options before the main scan command.
-.new
.cindex &`pass_unscanned`& "avast"
If &`pass_unscanned`&
is set, any files the Avast scanner can't scan (e.g.
decompression bombs, or invalid archives) are considered clean. Use with
care.
-.wen
For example:
.code
.vitem &%aveserver%&
.cindex "virus scanners" "Kaspersky"
This is the scanner daemon of Kaspersky Version 5. You can get a trial version
-at &url(http://www.kaspersky.com). This scanner type takes one option,
+at &url(https://www.kaspersky.com/). This scanner type takes one option,
which is the path to the daemon's UNIX socket. The default is shown in this
example:
.code
.vitem &%clamd%&
.cindex "virus scanners" "clamd"
This daemon-type scanner is GPL and free. You can get it at
-&url(http://www.clamav.net/). Some older versions of clamd do not seem to
+&url(https://www.clamav.net/). Some older versions of clamd do not seem to
unpack MIME containers, so it used to be recommended to unpack MIME attachments
in the MIME ACL. This is no longer believed to be necessary.
.endd
.vitem &%drweb%&
.cindex "virus scanners" "DrWeb"
-The DrWeb daemon scanner (&url(http://www.sald.com/)) interface
+The DrWeb daemon scanner (&url(https://www.sald.ru/)) interface
takes one option,
either a full path to a UNIX socket,
or host and port specifiers separated by white space.
.vitem &%fsecure%&
.cindex "virus scanners" "F-Secure"
-The F-Secure daemon scanner (&url(http://www.f-secure.com)) takes one
+The F-Secure daemon scanner (&url(https://www.f-secure.com/)) takes one
argument which is the path to a UNIX socket. For example:
.code
av_scanner = fsecure:/path/to/.fsav
.vitem &%mksd%&
.cindex "virus scanners" "mksd"
-This is a daemon type scanner that is aimed mainly at Polish users, though some
-parts of documentation are now available in English. You can get it at
-&url(http://linux.mks.com.pl/). The only option for this scanner type is
+This was a daemon type scanner that is aimed mainly at Polish users,
+though some documentation was available in English.
+The history can be shown at &url(https://en.wikipedia.org/wiki/Mks_vir)
+and this appears to be a candidate for removal from Exim, unless
+we are informed of other virus scanners which use the same protocol
+to integrate.
+The only option for this scanner type is
the maximum number of processes used simultaneously to scan the attachments,
provided that mksd has
been run with at least the same number of child processes. For example:
.vitem &%sophie%&
.cindex "virus scanners" "Sophos and Sophie"
Sophie is a daemon that uses Sophos' &%libsavi%& library to scan for viruses.
-You can get Sophie at &url(http://www.clanfield.info/sophie/). The only option
+You can get Sophie at &url(http://sophie.sourceforge.net/). The only option
for this scanner type is the path to the UNIX socket that Sophie uses for
client communication. For example:
.code
For more information about installation and configuration of SpamAssassin or
Rspamd refer to their respective websites at
-&url(http://spamassassin.apache.org) and &url(http://www.rspamd.com)
+&url(https://spamassassin.apache.org/) and &url(https://www.rspamd.com/)
SpamAssassin can be installed with CPAN by running:
.code
.section "Building Exim to use a local scan function" "SECID207"
.cindex "&[local_scan()]& function" "building Exim to use"
To make use of the local scan function feature, you must tell Exim where your
-function is before building Exim, by setting LOCAL_SCAN_SOURCE in your
+function is before building Exim, by setting
+.new
+both HAVE_LOCAL_SCAN and
+.wen
+LOCAL_SCAN_SOURCE in your
&_Local/Makefile_&. A recommended place to put it is in the &_Local_&
directory, so you might set
.code
+HAVE_LOCAL_SCAN=yes
LOCAL_SCAN_SOURCE=Local/local_scan.c
.endd
for example. The function must be called &[local_scan()]&. It is called by
.cindex "VERP"
.cindex "Variable Envelope Return Paths"
.cindex "envelope sender"
-Variable Envelope Return Paths &-- see &url(http://cr.yp.to/proto/verp.txt) &--
+Variable Envelope Return Paths &-- see &url(https://cr.yp.to/proto/verp.txt) &--
are a way of helping mailing list administrators discover which subscription
address is the cause of a particular delivery failure. The idea is to encode
the original recipient address in the outgoing envelope sender address, so that
&`F `& sender address (on delivery lines)
&`H `& host name and IP address
&`I `& local interface used
-&`K `& CHUNKING extension used
&`id `& message id for incoming message
+&`K `& CHUNKING extension used
+&`L `& on &`<=`& and &`=>`& lines: PIPELINING extension used
&`M8S `& 8BITMIME status for incoming message
&`P `& on &`<=`& lines: protocol used
&` `& on &`=>`& and &`**`& lines: return path
failed. The delivery was discarded.
.endlist olist
.next
-.new
.cindex DKIM "log line"
&'DKIM: d='&&~&~Verbose results of a DKIM verification attempt, if enabled for
logging and the message has a DKIM signature header.
-.wen
.endlist ilist
&` queue_time `& time on queue for one recipient
&` queue_time_overall `& time on queue for whole message
&` pid `& Exim process id
+&` pipelining `& PIPELINING use, on <= and => lines
&` proxy `& proxy address on <= and => lines
&` receive_time `& time taken to receive message
&` received_recipients `& recipients on <= lines
&%delivery_size%&: For each delivery, the size of message delivered is added to
the &"=>"& line, tagged with S=.
.next
-.new
.cindex log "DKIM verification"
.cindex DKIM "verification logging"
&%dkim%&: For message acceptance log lines, when an DKIM signature in the header
.cindex log "DKIM verification"
.cindex DKIM "verification logging"
&%dkim_verbose%&: A log entry is written for each attempted DKIM verification.
-.wen
.next
.cindex "log" "dnslist defer"
.cindex "DNS list" "logging defer"
&%pid%&: The current process id is added to every log line, in square brackets,
immediately after the time and date.
.next
+.new
+.cindex log pipelining
+.cindex pipelining "logging outgoing"
+&%pipelining%&: A field is added to delivery and accept
+log lines when the ESMTP PIPELINING extension was used.
+The field is a single "L".
+
+On accept lines, where PIPELINING was offered but not used by the client,
+the field has a minus appended.
+.next
.cindex "log" "queue run"
.cindex "queue runner" "logging"
&%queue_run%&: The start and end of every queue run are logged.
the local host is logged as QT=<&'time'&> on &"Completed"& lines, for
example, &`QT=3m45s`&. The clock starts when Exim starts to receive the
message, so it includes reception time as well as the total delivery time.
-.new
.next
.cindex "log" "receive duration"
&%receive_time%&: For each message, the amount of real time it has taken to
perform the reception is logged as RT=<&'time'&>, for example, &`RT=1s`&.
If millisecond logging is enabled, short times will be shown with greater
precision, eg. &`RT=0.204s`&.
-.wen
.next
.cindex "log" "recipients"
&%received_recipients%&: The recipients of a message are listed in the main log
&%tls_certificate_verified%&: An extra item is added to <= and => log lines
when TLS is in use. The item is &`CV=yes`& if the peer's certificate was
verified
-.new
using a CA trust anchor,
&`CA=dane`& if using a DNS trust anchor,
-.wen
and &`CV=no`& if not.
.next
.cindex "log" "TLS cipher"
Another utility that might be of use to sites with many MTAs is Tom Kistner's
&'exilog'&. It provides log visualizations across multiple Exim servers. See
-&url(http://duncanthrax.net/exilog/) for details.
+&url(https://duncanthrax.net/exilog/) for details.
.cindex "&'eximstats'&"
A Perl script called &'eximstats'& is provided for extracting statistical
information from log files. The output is either plain text, or HTML.
-Exim log files are also supported by the &'Lire'& system produced by the
-LogReport Foundation &url(http://www.logreport.org).
+. --- 2018-09-07: LogReport's Lire appears to be dead; website is a Yahoo Japan
+. --- 404 error and everything else points to that.
The &'eximstats'& script has been hacked about quite a bit over time. The
latest version is the result of some extensive revision by Steve Campbell. A
is insurance against disk crashes where the directory is lost but the files
themselves are recoverable.
+.new
+The file formats may be changed, or new formats added, at any release.
+Spool files are not intended as an interface to other programs
+and should not be used as such.
+.wen
+
Some people are tempted into editing -D files in order to modify messages. You
need to be extremely careful if you do this; it is not recommended and you are
on your own if you do it. Here are some of the pitfalls:
be tracked on a per-domain basis, rather than merely upon source IP address.
DKIM is documented in RFC 6376.
-.new
As DKIM relies on the message being unchanged in transit, messages handled
by a mailing-list (which traditionally adds to the message) will not match
any original DKIM signature.
-.wen
DKIM support is compiled into Exim by default if TLS support is present.
It can be disabled by setting DISABLE_DKIM=yes in &_Local/Makefile_&.
default "policy". Instead it enables you to build your own policy using
Exim's standard controls.
-.new
Please note that verification of DKIM signatures in incoming mail is turned
on by default for logging (in the <= line) purposes.
c=relaxed/relaxed a=rsa-sha1
i=@facebookmail.com t=1252484542 [verification succeeded]
.endd
-.wen
You might want to turn off DKIM verification processing entirely for internal
or relay mail sources. To do that, set the &%dkim_disable_verify%& ACL
.section "Signing outgoing messages" "SECDKIMSIGN"
.cindex "DKIM" "signing"
-.new
For signing to be usable you must have published a DKIM record in DNS.
Note that RFC 8301 says:
.code
for the former it is the base64 of the ASN.1 for the RSA public key
(equivalent to the private-key .pem with the header/trailer stripped)
but for EC keys it is the base64 of the pure key; no ASN.1 wrapping.
-.wen
Signing is enabled by setting private options on the SMTP transport.
These options take (expandable) strings as arguments.
The result can either
.ilist
be a valid RSA private key in ASCII armor (.pem file), including line breaks
-.new
.next
with GnuTLS 3.6.0 or OpenSSL 1.1.1 or later,
be a valid Ed25519 private key (same format as above)
-.wen
.next
start with a slash, in which case it is treated as a file that contains
the private key
is set.
.endlist
-.new
To generate keys under OpenSSL:
.code
openssl genrsa -out dkim_rsa.private 2048
Note that the format
of Ed25519 keys in DNS has not yet been decided; this release supports
both of the leading candidates at this time, a future release will
-probably drop support for whichever proposal loses
-.wen
+probably drop support for whichever proposal loses.
.option dkim_hash smtp string&!! sha256
-.new
Can be set to any one of the supported hash methods, which are:
.ilist
&`sha1`& &-- should not be used, is old and insecure
.next
&`sha512`& &-- possibly more secure but less well supported
.endlist
-.wen
-.new
Note that RFC 8301 says:
.code
rsa-sha1 MUST NOT be used for signing or verifying.
.endd
-.wen
.option dkim_identity smtp string&!! unset
If set after expansion, the value is used to set an "i=" tag in
This option sets the canonicalization method used when signing a message.
The DKIM RFC currently supports two methods: "simple" and "relaxed".
The option defaults to "relaxed" when unset. Note: the current implementation
-only supports using the same canonicalization method for both headers and body.
+only supports signing with the same canonicalization method for both headers and body.
.option dkim_strict smtp string&!! unset
This option defines how Exim behaves when signing a message that
will be signed, and one signature added for a missing header with the
name will be appended.
+.new
+.option dkim_timestamps smtp integer&!! unset
+This option controls the inclusion of timestamp information in the signature.
+If not set, no such information will be included.
+Otherwise, must be an unsigned number giving an offset in seconds from the current time
+for the expiry tag
+(eg. 1209600 for two weeks);
+both creation (t=) and expiry (x=) tags will be included.
+
+RFC 6376 lists these tags as RECOMMENDED.
+.wen
+
.section "Verifying DKIM signatures in incoming mail" "SECDKIMVFY"
.cindex "DKIM" "verification"
-Verification of DKIM signatures in SMTP incoming email is implemented via the
-&%acl_smtp_dkim%& ACL. By default, this ACL is called once for each
+.new
+Verification of DKIM signatures in SMTP incoming email is done for all
+messages for which an ACL control &%dkim_disable_verify%& has not been set.
+.cindex authentication "expansion item"
+Performing verification sets up information used by the
+&$authresults$& expansion item.
+.wen
+
+.new The results of that verification are then made available to the
+&%acl_smtp_dkim%& ACL, &new(which can examine and modify them).
+By default, this ACL is called once for each
syntactically(!) correct signature in the incoming message.
A missing ACL definition defaults to accept.
If any ACL call does not accept, the message is not accepted.
If a cutthrough delivery was in progress for the message, that is
summarily dropped (having wasted the transmission effort).
-To evaluate the signature in the ACL a large number of expansion variables
+To evaluate the &new(verification result) in the ACL
+a large number of expansion variables
containing the signature status and its details are set up during the
runtime of the ACL.
-.new
-.cindex authentication "expansion item"
-Performing verification sets up information used by the
-&$authresults$& expansion item.
-.wen
-
Calling the ACL only for existing signatures is not sufficient to build
more advanced policies. For that reason, the global option
&%dkim_verify_signers%&, and a global expansion variable
This might, for instance, be done to enforce a policy restriction on
hash-method or key-size:
.code
- warn condition = ${if eq {$dkim_verify_status}{pass}}
- condition = ${if eq {$len_3:$dkim_algo}{rsa}}
- condition = ${if or {eq {$dkim_algo}{rsa-sha1}} \
- {< {$dkim_key_length}{1024}} }
- logwrite = NOTE: forcing dkim verify fail (was pass)
- set dkim_verify_status = fail
- set dkim_verify_reason = hash too weak or key too short
+ warn condition = ${if eq {$dkim_verify_status}{pass}}
+ condition = ${if eq {${length_3:$dkim_algo}}{rsa}}
+ condition = ${if or {{eq {$dkim_algo}{rsa-sha1}} \
+ {< {$dkim_key_length}{1024}}}}
+ logwrite = NOTE: forcing DKIM verify fail (was pass)
+ set dkim_verify_status = fail
+ set dkim_verify_reason = hash too weak or key too short
.endd
-After all the DKIM ACL runs have completed, the value becomes a
+So long as a DKIM ACL is defined (it need do no more than accept),
+after all the DKIM ACL runs have completed, the value becomes a
colon-separated list of the values after each run.
+This is maintained for the mime, prdr and data ACLs.
.vitem &%$dkim_verify_reason%&
A string giving a little bit more detail when &%$dkim_verify_status%& is either
.vitem &%$dkim_algo%&
The algorithm used. One of 'rsa-sha1' or 'rsa-sha256'.
-.new
If running under GnuTLS 3.6.0 or OpenSSL 1.1.1 or later,
may also be 'ed25519-sha256'.
The "_CRYPTO_SIGN_ED25519" macro will be defined if support is present
for EC keys.
-.wen
-.new
Note that RFC 8301 says:
.code
rsa-sha1 MUST NOT be used for signing or verifying.
To enforce this you must have a DKIM ACL which checks this variable
and overwrites the &$dkim_verify_status$& variable as discussed above.
-.wen
.vitem &%$dkim_canon_body%&
The body canonicalization method. One of 'relaxed' or 'simple'.
The number of signed body bytes. If zero ("0"), the body is unsigned. If no
limit was set by the signer, "9999999999999" is returned. This makes sure
that this variable always expands to an integer value.
+.new
+&*Note:*& The presence of the signature tag specifying a signing body length
+is one possible route to spoofing of valid DKIM signatures.
+A paranoid implementation might wish to regard signature where this variable
+shows less than the "no limit" return as being invalid.
+.wen
.vitem &%$dkim_created%&
UNIX timestamp reflecting the date and time when the signature was created.
signature to be treated as "expired". When this was not specified by the
signer, "9999999999999" is returned. This makes it possible to do useful
integer size comparisons against this value.
-.new
Note that Exim does not check this value.
-.wen
.vitem &%$dkim_headernames%&
A colon-separated list of names of headers included in the signature.
.vitem &%$dkim_key_length%&
Number of bits in the key.
-.new
Note that RFC 8301 says:
.code
Verifiers MUST NOT consider signatures using RSA keys of
To enforce this you must have a DKIM ACL which checks this variable
and overwrites the &$dkim_verify_status$& variable as discussed above.
As EC keys are much smaller, the check should only do this for RSA keys.
-.wen
.endlist
-.new
.section "SPF (Sender Policy Framework)" SECSPF
.cindex SPF verification
SPF is a mechanism whereby a domain may assert which IP addresses may transmit
messages with its domain in the envelope from, documented by RFC 7208.
For more information on SPF see &url(http://www.openspf.org).
+. --- 2018-09-07: still not https
Messages sent by a system not authorised will fail checking of such assertions.
This includes retransmissions done by traditional forwarders.
SPF verification support is built into Exim if SUPPORT_SPF=yes is set in
&_Local/Makefile_&. The support uses the &_libspf2_& library
-&url(http://www.libspf2.org/).
+&url(https://www.libspf2.org/).
There is no Exim involvement in the transmission of messages;
publishing certain DNS records is all that is required.
For verification, an ACL condition and an expansion lookup are provided.
-.new
.cindex authentication "expansion item"
Performing verification sets up information used by the
&$authresults$& expansion item.
-.wen
.cindex SPF "ACL condition"
capability.
Refer to &url(http://www.openspf.org/FAQ/Best_guess_record)
for a description of what it means.
+. --- 2018-09-07: still not https:
To access this feature, simply use the spf_guess condition in place
of the spf one. For example:
Currently, only IPv4 addresses are supported.
-. wen-for SPF section
-.wen
. ////////////////////////////////////////////////////////////////////////////
To include this support, include &"SUPPORT_PROXY=yes"&
in Local/Makefile.
-It was built on specifications from:
-(&url(http://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt)).
-That URL was revised in May 2014 to version 2 spec:
-(&url(http://git.1wt.eu/web?p=haproxy.git;a=commitdiff;h=afb768340c9d7e50d8e)).
+It was built on the HAProxy specification, found at
+&url(https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt).
The purpose of this facility is so that an application load balancer,
such as HAProxy, can sit in front of several Exim servers
.cindex utf8 "address downconversion"
.cindex i18n "utf8 address downconversion"
-.new
The RCPT ACL
-.wen
may use the following modifier:
.display
control = utf8_downconvert
If mua_wrapper is set, the utf8_downconvert control
is initially set to -1.
+.new
+The smtp transport has an option &%utf8_downconvert%&.
+If set it must expand to one of the three values described above,
+and it overrides any previously set value.
+.wen
+
There is no explicit support for VRFY and EXPN.
Configurations supporting these should inspect
.display
&`dane:fail `& failure reason
&`msg:delivery `& smtp confirmation message
+&`msg:fail:internal `& failure reason
+&`msg:fail:delivery `& smtp error message
&`msg:rcpt:host:defer `& error string
&`msg:rcpt:defer `& error string
&`msg:host:defer `& error string
git://git.exim.org / users / jgh / exim.git / blobdiff