.section "FTP and web sites" "SECID2"
.cindex "web site"
.cindex "FTP site"
-The primary site for Exim source distributions is currently the University of
-Cambridge's FTP site, whose contents are described in &'Where to find the Exim
-distribution'& below. In addition, there is a web site and an FTP site at
-&%exim.org%&. These are now also hosted at the University of Cambridge. The
-&%exim.org%& site was previously hosted for a number of years by Energis
-Squared, formerly Planet Online Ltd, whose support I gratefully acknowledge.
+.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"
online information is the Exim wiki (&url(http://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"
.section "Where to find the Exim distribution" "SECTavail"
.cindex "FTP site"
+.cindex "HTTPS download site"
.cindex "distribution" "ftp site"
-The master ftp site for the Exim distribution is
+.cindex "distribution" "https site"
+.new
+The master distribution site for the Exim distribution is
.display
-&*ftp://ftp.exim.org/pub/exim*&
+&*https://downloads.exim.org/*&
.endd
-The file references that follow are relative to the &_exim_& directories at
-these sites. There are now quite a number of independent mirror sites around
+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'&.
+
+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_&.
-Within the &_exim_& directory there are subdirectories called &_exim3_& (for
+Within the top exim directory there are subdirectories called &_exim3_& (for
previous Exim 3 distributions), &_exim4_& (for the latest Exim 4
distributions), and &_Testing_& for testing versions. In the &_exim4_&
subdirectory, the current release can always be found in files called
.display
+&_exim-n.nn.tar.xz_&
&_exim-n.nn.tar.gz_&
&_exim-n.nn.tar.bz2_&
.endd
-where &'n.nn'& is the highest such version number in the directory. The two
+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.
-The &_.bz2_& file is usually a lot smaller than the &_.gz_& file.
+.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'&.
-At time of last update, releases were being made by Phil Pennock and signed with
-key &'0x403043153903637F'&, although that key is expected to be replaced in 2013.
-A trust path from Nigel's key to Phil's can be observed at
-&url(https://www.security.spodhuis.org/exim-trustpath).
-
-Releases have also been authorized to be performed by Todd Lyons who signs with
-key &'0xC4F4F94804D29EBA'&. A direct trust path exists between previous RE Phil
-Pennock and Todd Lyons through a common associate.
+.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-n.nn.tar.xz.asc_&
&_exim-n.nn.tar.gz.asc_&
&_exim-n.nn.tar.bz2.asc_&
.endd
&_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_& as well as &_.gz_& forms.
+distribution, and are also available in &_.bz2_& and &_.xz_& forms.
+.wen
.section "Limitations" "SECID6"
.vitem &%-MCK%&
.oindex "&%-MCK%&"
This option is not intended for use by external callers. It is used internally
-by Exim in conjunction with the &%-MC%& option. It signifies that an
+by Exim in conjunction with the &%-MC%& option. It signifies that a
remote host supports the ESMTP &_CHUNKING_& extension.
.vitem &%-MCP%&
master/slave replication, the list must contain all the master and slave
servers.
-When the Redis Cluster returns a "MOVED" response to a query, exim does not
+When the Redis Cluster returns a "MOVED" response to a query, Exim does not
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.
.vitem "&*${authresults{*&<&'authserv-id'&>&*}}*&"
.cindex authentication "results header"
.cindex headers "authentication-results:"
+.cindex authentication "expansion item"
This item returns a string suitable for insertion as an
&'Authentication-Results"'&
header line.
The given <&'authserv-id'&> is included in the result; typically this
-will ba a domain name identifying the system performing the authentications.
-Methods that may be present in the result include:
+will be a domain name identifying the system performing the authentications.
+Methods that might be present in the result include:
.code
none
iprev
.code
add_header = :at_start:${authresults {$primary_hostname}}
.endd
+This is safe even if no authentication results are available.
.wen
user/password authenticator configuration might preserve the user name for use
in the routers. Note that this is not the same information that is saved in
&$sender_host_authenticated$&.
+
When a message is submitted locally (that is, not over a TCP connection)
the value of &$authenticated_id$& is normally the login name of the calling
process. However, a trusted user can override this by means of the &%-oMai%&
command line option.
+.new
+This second case also sets up inforamtion used by the
+&$authresults$& expansion item.
+.wen
.vitem &$authenticated_fail_id$&
.cindex "authentication" "fail" "id"
the result, the name is not accepted, and &$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$&
.vindex "&$host_lookup_failed$&"
See &$host_lookup_deferred$&.
.vitem &$spf_header_comment$& &&&
&$spf_received$& &&&
&$spf_result$& &&&
+ &$spf_result_guessed$& &&&
&$spf_smtp_comment$&
These variables are only available if Exim is built with SPF support.
For details see section &<<SECSPF>>&.
&%certextract%& expansion item, &%md5%&, &%sha1%& or &%sha256%& operator,
or a &%def%& condition.
-&*Note*&: Under current versions of OpenSSL, when a list of more than one
+&*Note*&: Under versions of OpenSSL preceding 1.1.1,
+when a list of more than one
file is used for &%tls_certificate%&, this variable is not reliable.
.vitem &$tls_in_peercert$&
.option spool_wireformat main boolean false
.cindex "spool directory" "file formats"
-If this option is set, Exim may for some messages use an alternate format
+If this option is set, Exim may for some messages use an alternative format
for data-files in the spool which matches the wire format.
Doing this permits more efficient message reception and transmission.
-Currently it is only done for messages received using the EMSTP CHUNKING
+Currently it is only done for messages received using the ESMTP CHUNKING
option.
The following variables will not have useful values:
Users of the local_scan() API (see &<<CHAPlocalscan>>&),
and any external programs which are passed a reference to a message data file
(except via the &"regex"&, &"malware"& or &"spam"&) ACL conditions)
-will need to be aware of the potential different format.
+will need to be aware of the different formats potentially available.
Using any of the ACL conditions noted will negate the reception benefit
(as a Unix-mbox-format file is constructed for them).
&*Note*&: If you use filenames based on IP addresses, change the list
separator in the usual way to avoid confusion under IPv6.
-&*Note*&: Under current versions of OpenSSL, when a list of more than one
+&*Note*&: Under versions of OpenSSL preceding 1.1.1,
+when a list of more than one
file is used, the &$tls_in_ourcert$& variable is unreliable.
&*Note*&: OCSP stapling is not usable under OpenSSL
option.
+.new
+.option dane_require_tls_ciphers smtp string&!! unset
+.cindex "TLS" "requiring specific ciphers for DANE"
+.cindex "cipher" "requiring specific"
+.cindex DANE "TLS ciphers"
+This option may be used to override &%tls_require_ciphers%& for connections
+where DANE has been determined to be in effect.
+If not set, then &%tls_require_ciphers%& will be used.
+Normal SMTP delivery is not able to make strong demands of TLS cipher
+configuration, because delivery will fall back to plaintext. Once DANE has
+been determined to be in effect, there is no plaintext fallback and making the
+TLS cipherlist configuration stronger will increase security, rather than
+counter-intuitively decreasing it.
+If the option expands to be empty or is forced to fail, then it will
+be treated as unset and &%tls_require_ciphers%& will be used instead.
+.wen
+
+
.option data_timeout smtp time 5m
This sets a timeout for the transmission of each block in the data portion of
the message. As a result, the overall timeout for a message depends on the size
client from which the message was received. This variable is empty if there was
no successful authentication.
+.new
+.cindex authentication "expansion item"
+Successful authentication sets up information used by the
+&$authresults$& expansion item.
+.wen
+
Note that the hostlist test for whether to do authentication can be
confused if name-IP lookups change between the time the peer is decided
-on and the transport running. For example, with a manualroute
-router given a host name, and DNS "round-robin" use by that name: if
+upon and the time that the transport runs. For example, with a manualroute
+router given a host name, and with DNS "round-robin" used by that name: if
the local resolver cache times out between the router and the transport
running, the transport may get an IP for the name for its authentication
check which does not match the connection peer IP.
contentious. As of RFC 8314, the common practice of using the historically
allocated port 465 for "email submission but with TLS immediately upon connect
instead of using STARTTLS" is officially blessed by the IETF, and recommended
-in preference to STARTTLS.
+by them in preference to STARTTLS.
The name originally assigned to the port was &"ssmtp"& or &"smtps"&, but as
clarity emerged over the dual roles of SMTP, for MX delivery and Email
reassigned for other use.
Thus you may encounter guidance claiming that you shouldn't enable use of
this port.
-In practice, a number of mail-clients have only supported submissions, not
-submission with STARTTLS upgrade.
+In practice, a number of mail-clients have only ever supported submissions,
+not submission with STARTTLS upgrade.
Ideally, offer both submission (587) and submissions (465) service.
Exim supports TLS-on-connect by means of the &%tls_on_connect_ports%&
to this server, its A record, its TLSA record and any associated CNAME records must all be covered by
DNSSEC.
2) add TLSA DNS records. These say what the server certificate for a TLS connection should be.
-3) offer a server certificate, or certificate chain, in TLS connections which is traceable to the one
-defined by (one of?) the TSLA records
+3) offer a server certificate, or certificate chain, in TLS connections which is is anchored by one of the TLSA records.
There are no changes to Exim specific to server-side operation of DANE.
Support for client-side operation of DANE can be included at compile time by defining SUPPORT_DANE=yes
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.
+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.
+
The TLSA record should have a Selector field of SPKI(1) and a Matching Type field of SHA2-512(2).
At the time of writing, &url(https://www.huque.com/bin/gen_tlsa)
those who use &%hosts_require_ocsp%&, should consider the interaction with DANE in their OCSP settings.
-For client-side DANE there are two new smtp transport options, &%hosts_try_dane%& and &%hosts_require_dane%&.
-The latter variant will result in failure if the target host is not DNSSEC-secured.
+For client-side DANE there are three new smtp transport options, &%hosts_try_dane%&, &%hosts_require_dane%&
+and &%dane_require_tls_ciphers%&.
+The require variant will result in failure if the target host is not DNSSEC-secured.
DANE will only be usable if the target host has DNSSEC-secured MX, A and TLSA records.
will be required for the host. If it does not, the host will not
be used; there is no fallback to non-DANE or non-TLS.
+If DANE is requested and usable, then the TLS cipher list configuration
+prefers to use the option &%dane_require_tls_ciphers%& and falls
+back to &%tls_require_ciphers%& only if that is unset.
+This lets you configure "decent crypto" for DANE and "better than nothing
+crypto" as the default. Note though that while GnuTLS lets the string control
+which versions of TLS/SSL will be negotiated, OpenSSL does not and you're
+limited to ciphersuite constraints.
+
If DANE is requested and useable (see above) the following transport options are ignored:
.code
hosts_require_tls
Section 4.3 of that document.
Under GnuTLS, DANE is only supported from version 3.0.0 onwards.
+
+DANE is specified in published RFCs and decouples certificate authority trust
+selection from a "race to the bottom" of "you must trust everything for mail
+to get through". There is an alternative technology called MTA-STS, which
+instead publishes MX trust anchor information on an HTTPS website. At the
+time this text was last updated, MTA-STS was still a draft, not yet an RFC.
+Exim has no support for MTA-STS as a client, but Exim mail server operators
+can choose to publish information describing their TLS configuration using
+MTA-STS to let those clients who do use that protocol derive trust
+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.
+
+The most interoperable course of action is probably to use
+&url(https://letsencrypt.org/,Let's Encrypt), with automated certificate
+renewal; to publish the anchor information in DNSSEC-secured DNS via TLSA
+records for DANE clients (such as Exim and Postfix) and to publish anchor
+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
Note also that headers cannot be
modified by any of the post-data ACLs (DATA, MIME and DKIM).
Headers may be modified by routers (subject to the above) and transports.
-The Received-By: header is generated as soon as the body reception starts,
+The &'Received-By:'& header is generated as soon as the body reception starts,
rather than the traditional time after the full message is received;
this will affect the timestamp.
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 : \
before use.
The usual list-parsing of the content (see &<<SECTlistconstruct>>&) applies.
The following scanner types are supported in this release,
-.new
though individual ones can be included or not at build time:
-.wen
.vlist
.vitem &%avast%&
or host and port specifiers separated by white space.
The host may be a name or an IP address; the port is either a
single number or a pair of numbers with a dash between.
-Any further options are given, on separate lines,
-to the daemon as options before the main scan command.
+A list of options may follow. These options are interpreted on the
+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
av_scanner = avast:/var/run/avast/scan.sock:FLAGS -fullfiles:SENSITIVITY -pup
+av_scanner = avast:/var/run/avast/scan.sock:pass_unscanned:FLAGS -fullfiles:SENSITIVITY -pup
av_scanner = avast:192.168.2.22 5036
.endd
If you omit the argument, the default path
PACK
.endd
-Only the first virus detected will be reported.
-
+If the scanner returns a temporary failure (e.g. license issues, or
+permission problems), the message is deferred and a paniclog entry is
+written. The usual &`defer_ok`& option is available.
.vitem &%aveserver%&
.cindex "virus scanners" "Kaspersky"
If the value of av_scanner points to a UNIX socket file or contains the
&`local`&
option, then the ClamAV interface will pass a filename containing the data
-to be scanned, which will should normally result in less I/O happening and be
+to be scanned, which should normally result in less I/O happening and be
more efficient. Normally in the TCP case, the data is streamed to ClamAV as
Exim does not assume that there is a common filesystem with the remote host.
.code
av_scanner = f-protd:localhost 10200-10204
.endd
-If you omit the argument, the default values show above are used.
+If you omit the argument, the default values shown above are used.
.vitem &%f-prot6d%&
.cindex "virus scanners" "f-prot6d"
&` queue_time_overall `& time on queue for whole message
&` pid `& Exim process id
&` proxy `& proxy address on <= and => lines
+&` receive_time `& time taken to receive message
&` received_recipients `& recipients on <= lines
&` received_sender `& sender on <= lines
&`*rejected_header `& header contents on reject log
.endlist
.new
+To generate keys under OpenSSL:
+.code
+openssl genrsa -out dkim_rsa.private 2048
+openssl rsa -in dkim_rsa.private -out /dev/stdout -pubout -outform PEM
+.endd
+Take the base-64 lines from the output of the second command, concatenated,
+for the DNS TXT record.
+See section 3.6 of RFC6376 for the record specification.
+
+Under GnuTLS:
+.code
+certtool --generate-privkey --rsa --bits=2048 --password='' -8 --outfile=dkim_rsa.private
+certtool --load-privkey=dkim_rsa.private --pubkey-info
+.endd
+
Note that RFC 8301 says:
.code
Signers MUST use RSA keys of at least 1024 bits for all keys.
for some transition period.
The "_CRYPTO_SIGN_ED25519" macro will be defined if support is present
for EC keys.
+
+OpenSSL 1.1.1 and GnuTLS 3.6.0 can create Ed25519 private keys:
+.code
+openssl genpkey -algorithm ed25519 -out dkim_ed25519.private
+certtool --generate-privkey --key-type=ed25519 --outfile=dkim_ed25519.private
+.endd
+
+To produce the required public key value for a DNS record:
+.code
+openssl pkey -outform DER -pubout -in dkim_ed25519.private | tail -c +13 | base64
+certtool --load_privkey=dkim_ed25519.private --pubkey_info --outder | tail -c +13 | base64
+.endd
+
+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
.option dkim_hash smtp string&!! sha256
-Can be set alternatively to &"sha1"& to use an alternate hash
-method.
+.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
+&`sha256`& &-- the default
+.next
+&`sha512`& &-- possibly more secure but less well supported
+.endlist
+.wen
.new
Note that RFC 8301 says:
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}} \
+ {< {$dkim_key_length}{1024}}}}
+ logwrite = NOTE: forcing DKIM verify fail (was pass)
+ set dkim_verify_status = fail
+ set dkim_verify_reason = hash too weak or key too short
.endd
After all the DKIM ACL runs have completed, the value becomes a
SPF verification support is built into Exim if SUPPORT_SPF=yes is set in
&_Local/Makefile_&. The support uses the &_libspf2_& library
&url(http://www.libspf2.org/).
-There is no Exim involvement on the trasmission of messages; publishing certain
-DNS records is all that is required.
+There is no Exim involvement in the transmission of messages;
+publishing certain DNS records is all that is required.
For verification, an ACL condition and an expansion lookup are provided.
+.new
+.cindex authentication "expansion item"
+Performing verification sets up information used by the
+&$authresults$& expansion item.
+.wen
+
.cindex SPF "ACL condition"
.cindex ACL "spf condition"
.vitem &%permerror%&
This indicates a syntax error in the SPF record of the queried domain.
-You may deny messages when this occurs. (Changed in 4.83)
+You may deny messages when this occurs.
.vitem &%temperror%&
This indicates a temporary error during all processing, including Exim's
SPF processing. You may defer messages when this occurs.
-(Changed in 4.83)
-
-.vitem &%err_temp%&
-Same as permerror, deprecated in 4.83, will be removed in a future release.
-
-.vitem &%err_perm%&
-Same as temperror, deprecated in 4.83, will be removed in a future release.
.endlist
You can prefix each string with an exclamation mark to invert
one of pass, fail, softfail, none, neutral, permerror or
temperror.
+.vitem &$spf_result_guessed$&
+.vindex &$spf_result_guessed$&
+ This boolean is true only if a best-guess operation was used
+ and required in order to obtain a result.
+
.vitem &$spf_smtp_comment$&
.vindex &$spf_smtp_comment$&
This contains a string that can be used in a SMTP response
${lookup {username@domain} spf {ip.ip.ip.ip}}
.endd
-The lookup will return the same result strings as they can appear in
+The lookup will return the same result strings as can appear in
&$spf_result$& (pass,fail,softfail,neutral,none,err_perm,err_temp).
Currently, only IPv4 addresses are supported.
git://git.exim.org / exim.git / blobdiff