&*$h_*&<&'header&~name'&>&*:*&" &&&
"&*$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
${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:
.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"
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/_&.
.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>>&.
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 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:
.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"
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
+
.endd
-.section "Scanning with SpamAssassin and Rspamd" "SECTscanspamass"
+.section "Scanning with SpamAssassin" "SECTscanspamass"
.cindex "content scanning" "for spam"
.cindex "spam scanning"
.cindex "SpamAssassin"
-.cindex "Rspamd"
The &%spam%& ACL condition calls SpamAssassin's &%spamd%& daemon to get a spam
-score and a report for the message.
-Support is also provided for Rspamd.
-
-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)
-
-SpamAssassin can be installed with CPAN by running:
+score and a report for the message. You can get SpamAssassin at
+&url(http://www.spamassassin.org), or, if you have a working Perl
+installation, you can use CPAN by running:
.code
perl -MCPAN -e 'install Mail::SpamAssassin'
.endd
connection tracking may consider your half-closed connection as dead too
soon.
-
-To use Rspamd (which by default listens on all local addresses
-on TCP port 11333)
-you should add &%variant=rspamd%& after the address/port pair, for example:
-.code
-spamd_address = 127.0.0.1 11333 variant=rspamd
-.endd
-
As of version 2.60, &%SpamAssassin%& also supports communication over UNIX
sockets. If you want to us these, supply &%spamd_address%& with an absolute
file name instead of an address/port pair:
relevant if you have set up multiple SpamAssassin profiles. If you do not want
to scan using a specific profile, but rather use the SpamAssassin system-wide
default profile, you can scan for an unknown name, or simply use &"nobody"&.
-Rspamd does not use this setting. However, you must put something on the
-right-hand side.
+However, you must put something on the right-hand side.
The name allows you to use per-domain or per-user antispam profiles in
principle, but this is not straightforward in practice, because a message may
unencoded in headers.
.vitem &$spam_action$&
-For SpamAssassin either 'reject' or 'no action' depending on the
+Either 'reject' or 'no action' depending on the
spam score versus threshold.
-For Rspamd, the recommended action.
-
.endlist
The &%spam%& condition caches its results unless expansion 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.
-.cindex authentication "expansion item"
-Performing verification sets up information used by the
-&$authresults$& expansion item.
-
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
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.
git://git.exim.org / exim.git / blobdiff