X-Git-Url: https://git.exim.org/users/heiko/exim.git/blobdiff_plain/8473d4eebf594f883e8a198c990205fda5a25b77..214bab575a116231489f81bdb8e486352bd31392:/doc/doc-docbook/spec.xfpt diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index 015d7140e..7add7e604 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -1,4 +1,4 @@ -. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.34 2008/02/04 17:03:35 fanf2 Exp $ +. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.54 2009/10/13 08:46:06 tom Exp $ . . ///////////////////////////////////////////////////////////////////////////// . This is the primary source of the Exim Manual. It is an xfpt document that is @@ -172,17 +172,17 @@ Specification of the Exim Mail Transfer Agent The Exim MTA -23 August 2007 +09 June 2009 PhilipHazel PH University of Cambridge Computing Service
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England
- 4.68 - 23 August 2007 + 4.70 + 10 June 2009 PH -2007University of Cambridge +2009University of Cambridge .literal off @@ -431,8 +431,6 @@ directory are: .row &_exim.8_& "a man page of Exim's command line options" .row &_experimental.txt_& "documentation of experimental features" .row &_filter.txt_& "specification of the filter language" -.row &_pcrepattern.txt_& "specification of PCRE regular expressions" -.row &_pcretest.txt_& "specification of the PCRE testing program" .row &_Exim3.upgrade_& "upgrade notes from release 2 to release 3" .row &_Exim4.upgrade_& "upgrade notes from release 3 to release 4" .endtable @@ -732,10 +730,9 @@ A number of pieces of external code are included in the Exim distribution. .ilist Regular expressions are supported in the main Exim program and in the Exim monitor using the freely-distributable PCRE library, copyright -© University of Cambridge. The source to a cut down version of PCRE -used to be distributed in the directory &_src/pcre_&. However, this is -no longer the case and you will need to use a system PCRE library or -obtain and install the full version of the library from +© University of Cambridge. The source to PCRE is no longer shipped with +Exim, so you will need to use the version of PCRE shipped with your system, +or obtain and install the full version of the library from &url(ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre). .next .cindex "cdb" "acknowledgment" @@ -2226,9 +2223,8 @@ but this usage is deprecated. .cindex "installing Exim" "what is not installed" Running &'make install'& does not copy the Exim 4 conversion script -&'convert4r4'&, or the &'pcretest'& test program. You will probably run the -first of these only once (if you are upgrading from Exim 3), and the second -isn't really part of Exim. None of the documentation files in the &_doc_& +&'convert4r4'&. You will probably run this only once if you are +upgrading from Exim 3. None of the documentation files in the &_doc_& directory are copied, except for the info files when you have set INFO_DIRECTORY, as described in section &<>& below. @@ -4722,7 +4718,7 @@ up in a MySQL database. It helps to keep the file less cluttered if long strings such as SQL statements are defined separately as macros, for example: .code ALIAS_QUERY = select mailbox from user where \ - login=${quote_mysql:$local_part}; + login='${quote_mysql:$local_part}'; .endd This can then be used in a &(redirect)& router setting like this: .code @@ -5908,13 +5904,11 @@ Jeffrey Friedl's &'Mastering Regular Expressions'&, which is published by O'Reilly (see &url(http://www.oreilly.com/catalog/regex2/)). The documentation for the syntax and semantics of the regular expressions that -are supported by PCRE is included in plain text in the file -&_doc/pcrepattern.txt_& in the Exim distribution, and also in the HTML -tarbundle of Exim documentation. It describes in detail the features of the -regular expressions that PCRE supports, so no further description is included -here. The PCRE functions are called from Exim using the default option settings -(that is, with no PCRE options set), except that the PCRE_CASELESS option is -set when the matching is required to be case-insensitive. +are supported by PCRE is included in the PCRE distribution, and no further +description is included here. The PCRE functions are called from Exim using +the default option settings (that is, with no PCRE options set), except that +the PCRE_CASELESS option is set when the matching is required to be +case-insensitive. In most cases, when a regular expression is required in an Exim configuration, it has to start with a circumflex, in order to distinguish it from plain text @@ -5953,47 +5947,6 @@ $ is needed because string expansion also interprets dollar characters. -.section "Testing regular expressions" "SECID59" -.cindex "testing" "regular expressions" -.cindex "regular expressions" "testing" -.cindex "&'pcretest'&" -A program called &'pcretest'& forms part of the PCRE distribution and is built -with PCRE during the process of building Exim. It is primarily intended for -testing PCRE itself, but it can also be used for experimenting with regular -expressions. After building Exim, the binary can be found in the build -directory (it is not installed anywhere automatically). There is documentation -of various options in &_doc/pcretest.txt_&, but for simple testing, none are -needed. This is the output of a sample run of &'pcretest'&: -.display -&` re> `&&*&`/^([@]+)@.+\.(ac|edu)\.(?!kr)[a-z]{2}$/`&*& -&`data> `&&*&`x@y.ac.uk`&*& -&` 0: x@y.ac.uk`& -&` 1: x`& -&` 2: ac`& -&`data> `&&*&`x@y.ac.kr`&*& -&`No match`& -&`data> `&&*&`x@y.edu.com`&*& -&`No match`& -&`data> `&&*&`x@y.edu.co`&*& -&` 0: x@y.edu.co`& -&` 1: x`& -&` 2: edu`& -.endd -Input typed by the user is shown in bold face. After the &"re>"& prompt, a -regular expression enclosed in delimiters is expected. If this compiles without -error, &"data>"& prompts are given for strings against which the expression is -matched. An empty data line causes a new regular expression to be read. If the -match is successful, the captured substring values (that is, what would be in -the variables &$0$&, &$1$&, &$2$&, etc.) are shown. The above example tests for -an email address whose domain ends with either &"ac"& or &"edu"& followed by a -two-character top-level domain that is not &"kr"&. The local part is captured -in &$1$& and the &"ac"& or &"edu"& in &$2$&. - - - - - - . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// @@ -7219,13 +7172,13 @@ mysql_servers = slave1/db/name/pw:\ .endd In an updating lookup, you could then write: .code -${lookup mysql{servers=master; UPDATE ...} +${lookup mysql{servers=master; UPDATE ...} } .endd That query would then be sent only to the master server. If, on the other hand, the master is not to be used for reading, and so is not present in the global option, you can still update it by a query of this form: .code -${lookup pgsql{servers=master/db/name/pw; UPDATE ...} +${lookup pgsql{servers=master/db/name/pw; UPDATE ...} } .endd @@ -10763,7 +10716,7 @@ This is an obsolete name for &$received_port$&. .vitem &$item$& .vindex "&$item$&" This variable is used during the expansion of &*forall*& and &*forany*& -conditions (see section &<>&), and &*filter*&, &*man*&, and +conditions (see section &<>&), and &*filter*&, &*map*&, and &*reduce*& items (see section &<>&). In other circumstances, it is empty. @@ -19005,11 +18958,9 @@ filter itself, and the original process that reads the result and delivers it are all run in parallel, like a shell pipeline. The filter can perform any transformations it likes, but of course should take -care not to break RFC 2822 syntax. A demonstration Perl script is provided in -&_util/transport-filter.pl_&; this makes a few arbitrary modifications just to -show the possibilities. Exim does not check the result, except to test for a -final newline when SMTP is in use. All messages transmitted over SMTP must end -with a newline, so Exim supplies one if it is missing. +care not to break RFC 2822 syntax. Exim does not check the result, except to +test for a final newline when SMTP is in use. All messages transmitted over +SMTP must end with a newline, so Exim supplies one if it is missing. .cindex "content scanning" "per user" A transport filter can be used to provide content-scanning on a per-user basis @@ -23571,17 +23522,20 @@ login: driver = plaintext public_name = LOGIN server_prompts = Username:: : Password:: - server_condition = ${if ldapauth \ - {user="cn=${quote_ldap_dn:$auth1},ou=people,o=example.org" \ - pass=${quote:$auth2} \ - ldap://ldap.example.org/}} + server_condition = ${if and{{ + !eq{}{$auth1} }{ \ + ldapauth{user="cn=${quote_ldap_dn:$auth1},ou=people,o=example.org" \ + pass=${quote:$auth2} \ + ldap://ldap.example.org/} }} } server_set_id = uid=$auth1,ou=people,o=example.org .endd -Note the use of the &%quote_ldap_dn%& operator to correctly quote the DN for -authentication. However, the basic &%quote%& operator, rather than any of the -LDAP quoting operators, is the correct one to use for the password, because -quoting is needed only to make the password conform to the Exim syntax. At the -LDAP level, the password is an uninterpreted string. +We have to check that the username is not empty before using it, because LDAP +does not permit empty DN components. We must also use the &%quote_ldap_dn%& +operator to correctly quote the DN for authentication. However, the basic +&%quote%& operator, rather than any of the LDAP quoting operators, is the +correct one to use for the password, because quoting is needed only to make +the password conform to the Exim syntax. At the LDAP level, the password is an +uninterpreted string. @@ -24101,11 +24055,11 @@ sections &<>& and &<>&. .section "GnuTLS parameter computation" "SECID181" -GnuTLS uses RSA and D-H parameters that may take a substantial amount of time +GnuTLS uses D-H parameters that may take a substantial amount of time to compute. It is unreasonable to re-compute them for every TLS session. Therefore, Exim keeps this data in a file in its spool directory, called &_gnutls-params_&. The file is owned by the Exim user and is readable only by -its owner. Every Exim process that start up GnuTLS reads the RSA and D-H +its owner. Every Exim process that start up GnuTLS reads the D-H parameters from this file. If the file does not exist, the first Exim process that needs it computes the data and writes it to a temporary file which is renamed once it is complete. It does not matter if several Exim processes do @@ -24813,7 +24767,8 @@ connection is closed. In these special cases, the QUIT ACL does not run. .section "The not-QUIT ACL" "SECTNOTQUITACL" -The not-QUIT ACL, specified by &%smtp_notquit_acl%&, is run in most cases when +.vindex &$acl_smtp_notquit$& +The not-QUIT ACL, specified by &%acl_smtp_notquit%&, is run in most cases when an SMTP session ends without sending QUIT. However, when Exim itself is is bad trouble, such as being unable to write to its log files, this ACL is not run, because it might try to do things (such as write to log files) that make the @@ -25125,7 +25080,7 @@ the sending entity receives a &"success"& response. However, &%discard%& causes recipients to be discarded. If it is used in an ACL for RCPT, just the one recipient is discarded; if used for MAIL, DATA or in the non-SMTP ACL, all the message's recipients are discarded. Recipients that are discarded before DATA -do not appear in the log line when the &%log_recipients%& log selector is set. +do not appear in the log line when the &%received_recipients%& log selector is set. If the &%log_message%& modifier is set when &%discard%& operates, its contents are added to the line that is automatically written to the log. @@ -25515,7 +25470,8 @@ ACL fragment writes no logging information when access is denied: &` log_reject_target =`& .endd This modifier can be used in SMTP and non-SMTP ACLs. It applies to both -permanent and temporary rejections. +permanent and temporary rejections. Its effect lasts for the rest of the +current ACL. .vitem &*logwrite*&&~=&~<&'text'&> @@ -26361,7 +26317,9 @@ verified as a sender. .cindex "&ACL;" "testing a DNS list" In its simplest form, the &%dnslists%& condition tests whether the calling host is on at least one of a number of DNS lists by looking up the inverted IP -address in one or more DNS domains. For example, if the calling host's IP +address in one or more DNS domains. (Note that DNS list domains are not mail +domains, so the &`+`& syntax for named lists doesn't work - it is used for +special options instead.) For example, if the calling host's IP address is 192.168.62.43, and the ACL statement is .code deny dnslists = blackholes.mail-abuse.org : \ @@ -26938,7 +26896,7 @@ value. You can work out the time (the number of smoothing periods) that a client is subjected to counter-measures after an over-limit burst with this formula: .code -ln(peakrate/maxrate) + ln(peakrate/maxrate) .endd 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 @@ -27596,19 +27554,8 @@ the third string (in this case &"1"&), whether or not the cryptographic and timeout checks succeed. The &$prvscheck_result$& variable contains the result of the checks (empty for failure, &"1"& for success). -There are two more issues you must consider when implementing prvs-signing. -Firstly, you need to ensure that prvs-signed addresses are not blocked by your -ACLs. A prvs-signed address contains a slash character, but the default Exim -configuration contains this statement in the RCPT ACL: -.code -deny message = Restricted characters in address - domains = +local_domains - local_parts = ^[.] : ^.*[@%!/|] -.endd -This is a conservative rule that blocks local parts that contain slashes. You -should remove the slash in the last line. - -Secondly, you have to ensure that the routers accept prvs-signed addresses and +There is one more issue you must consider when implementing prvs-signing: +you have to ensure that the routers accept prvs-signed addresses and deliver them correctly. The easiest way to handle this is to use a &(redirect)& router to remove the signature with a configuration along these lines: .code @@ -34320,13 +34267,263 @@ unqualified domain &'foundation'&. .ecindex IIDforspo2 .ecindex IIDforspo3 +. //////////////////////////////////////////////////////////////////////////// +. //////////////////////////////////////////////////////////////////////////// + +.chapter "Support for DKIM (DomainKeys Identified Mail) - RFC4871" "CHID12" &&& + "DKIM Support" +.cindex "DKIM" + +Since version 4.70, DKIM support is compiled into Exim by default. It can be +disabled by setting DISABLE_DKIM=yes in Local/Makefile. + +Exim's DKIM implementation allows to +.olist +Sign outgoing messages: This function is implemented in the SMTP transport. +It can co-exist with all other Exim features, including transport filters. +.next +Verify signatures in incoming messages: This is implemented by an additional +ACL (acl_smtp_dkim), which can be called several times per message, with +different signature context. +.endlist + +In typical Exim style, the verification implementation does not include any +default "policy". Instead it enables you to build your own policy using +Exim's standard controls. + +Please note that verification of DKIM signatures in incoming mail is turned +on by default for logging purposes. For each signature in incoming email, +exim will log a line displaying the most important signature details, and the +signature status. Here is an example: +.code +2009-09-09 10:22:28 1MlIRf-0003LU-U3 DKIM: d=facebookmail.com s=q1-2009b c=relaxed/relaxed a=rsa-sha1 i=@facebookmail.com t=1252484542 [verification succeeded] +.endd +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 +control modifier. This should typically be done in the RCPT ACL, at points +where you accept mail from relay sources (internal hosts or authenticated +senders). + + +.section "Signing outgoing messages" "SECID513" +.cindex "DKIM" "signing" + +Signing is implemented by setting private options on the SMTP transport. +These options take (expandable) strings as arguments. + +.option dkim_domain smtp string&!! unset +MANDATORY +The domain you want to sign with. The result of this expanded +option is put into the &%$dkim_domain%& expansion variable. + +.option dkim_selector smtp string&!! unset +MANDATORY +This sets the key selector string. You can use the &%$dkim_domain%& expansion +variable to look up a matching selector. The result is put in the expansion +variable &%$dkim_selector%& which should be used in the &%dkim_private_key%& +option along with &%$dkim_domain%&. + +.option dkim_private_key smtp string&!! unset +MANDATORY +This sets the private key to use. You can use the &%$dkim_domain%& and +&%$dkim_selector%& expansion variables to determine the private key to use. +The result can either +.ilist +be a valid RSA private key in ASCII armor, including line breaks. +.next +start with a slash, in which case it is treated as a file that contains +the private key. +.next +be "0", "false" or the empty string, in which case the message will not +be signed. This case will not result in an error, even if &%dkim_strict%& +is set. +.endlist + +.option dkim_canon smtp string&!! unset +OPTIONAL +This option sets the canonicalization method used when signing a message. +The DKIM RFC currently supports two methods: "simple" and "relaxed". +The option defaults to "relaxed" when unset. Note: the current implementation +only supports using the same canonicalization method for both headers and body. + +.option dkim_strict smtp string&!! unset +OPTIONAL +This option defines how Exim behaves when signing a message that +should be signed fails for some reason. When the expansion evaluates to +either "1" or "true", Exim will defer. Otherwise Exim will send the message +unsigned. You can use the &%$dkim_domain%& and &%$dkim_selector%& expansion +variables here. + +.option dkim_sign_headers smtp string&!! unset +OPTIONAL +When set, this option must expand to (or be specified as) a colon-separated +list of header names. Headers with these names will be included in the message +signature. When unspecified, the header names recommended in RFC4871 will be +used. +.section "Verifying DKIM signatures in incoming mail" "SECID514" +.cindex "DKIM" "verification" + +Verification of DKIM signatures in incoming email is implemented via the +&%acl_smtp_dkim%& ACL. By default, this ACL is called once for each +syntactically(!) correct signature in the incoming message. + +To evaluate the signature in the ACL a large number of expansion variables +containing the signature status and its details are set up during the +runtime of the ACL. + +Calling the ACL only for existing signatures is not sufficient to build +more advanced policies. For that reason, the global option +&%dkim_verify_signers%&, and a global expansion variable +&%$dkim_signing_domains%& exist. + +The global option &%dkim_verify_signers%& can be set to a colon-separated +list of DKIM domains or identities for which the ACL &%acl_smtp_dkim%& is +called. It is expanded when the message has been received. At this point, +the expansion variable &%$dkim_signing_domains%& already contains a colon- +separated list of signer domains for the message. When &%dkim_verify_signers%& +is not specified in the main configuration, it defaults as: +.code +dkim_verify_signers = $dkim_signing_domains +.endd +This leads to the default behaviour of calling &%acl_smtp_dkim%& for each +DKIM signature in the message. Current DKIM verifiers may want to explicitly +call the ACL for known domains or identities. This would be achieved as follows: +.code +dkim_verify_signers = paypal.com:ebay.com:$dkim_signing_domains +.endd +This would result in &%acl_smtp_dkim%& always being called for "paypal.com" +and "ebay.com", plus all domains that have signatures in the message. You can +also be more creative in constructing your policy. Example: +.code +dkim_verify_signers = $sender_address_domain:$dkim_signing_domains +.endd + +Inside the &%acl_smtp_dkim%&, the following expansion variables are +available (from most to least important): + +.vlist +.vitem &%$dkim_verify_status%& +A string describing the general status of the signature. One of +.ilist +&%none%&: There is no signature in the message for the current domain or +identity. +.next +&%invalid%&: The signature could not be verified due to a processing error. +More detail is available in &%$dkim_verify_reason%&. +.next +&%fail%&: Verification of the signature failed. More detail is +available in &%$dkim_verify_reason%&. +.next +&%pass%&: The signature passed verification. It is valid. +.endlist +.vitem &%$dkim_verify_reason%& +A string giving a litte bit more detail when &%$dkim_verify_status%& is either +"fail" or "invalid". One of +.ilist +&%pubkey_unavailable%& (when &%$dkim_verify_status%&="invalid"): The public +key for the domain could not be retrieved. This may be a temporary problem. +.next +&%pubkey_syntax%& (when &%$dkim_verify_status%&="invalid"): The public key +record for the domain is syntactically invalid. +.next +&%bodyhash_mismatch%& (when &%$dkim_verify_status%&="fail"): The calculated +body hash does not match the one specified in the signature header. This +means that the message body was modified in transit. +.next +&%signature_incorrect%& (when &%$dkim_verify_status%&="fail"): The signature +could not be verified. This may mean that headers were modified, +re-written or otherwise changed in a way which is incompatible with +DKIM verification. It may of course also mean that the signature is forged. +.endlist +.vitem &%$dkim_domain%& +The signing domain. IMPORTANT: This variable is only populated if there is +ab actual signature in the message. It does NOT neccessarily carry the +domain that is currently being evaluated. Please use the &%dkim_signers%& ACL +condition for that. +.vitem &%$dkim_identity%& +The signing identity. IMPORTANT: This variable is only populated if there is +ab actual signature in the message. It does NOT neccessarily carry the +identity that is currently being evaluated. Please use the &%dkim_signers%& ACL +condition for that. +.vitem &%$dkim_selector%& +The key record selector string +.vitem &%$dkim_algo%& +The algorithm used. One of 'rsa-sha1' or 'rsa-sha256'. +.vitem &%$dkim_canon_body%& +The body canonicalization method. One of 'relaxed' or 'simple'. +.vitem &%dkim_canon_headers%& +The header canonicalization method. One of 'relaxed' or 'simple'. +.vitem &%$dkim_copiedheaders%& +A transcript of headers and their values which are included in the signature +(copied from the 'z=' tag of the signature). +.vitem &%$dkim_bodylength%& +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. +.vitem &%$dkim_created%& +UNIX timestamp reflecting the date and time when the signature was created. +When this was not specified by the signer, "0" is returned. +.vitem &%$dkim_expires%& +UNIX timestamp reflecting the date and time when the signer wants the +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. +.vitem &%$dkim_headernames%& +A colon-separated list of names of headers included in the signature. +.vitem &%$dkim_key_testing%& +"1" if the key record has the "testing" flag set, "0" if not. +.vitem &%$dkim_key_nosubdomaining%& +"1" if the key record forbids subdomaining, "0" otherwise. +.vitem &%$dkim_key_srvtype%& +Service type (tag s=) from the key record. Defaults to "*" if not specified +in the key record. +.vitem &%$dkim_key_granularity%& +Key granularity (tag g=) from the key record. Defaults to "*" if not specified +in the key record. +.vitem &%$dkim_key_notes%& +Notes from the key record (tag n=) +.endlist + +In addition, two ACL conditions are provided: + +.vlist +.vitem &%dkim_signers%& +ACL condition that checks a colon-separated list of domains or identities +for a match against the domain or identity that the ACL is currently verifying. +This is typically used to restrict an ACL verb to a group of domains or identities, like: + +.code +# Warn when message apparently from GMail has no signature at all +warn log_message = GMail sender without DKIM signature + sender_domains = gmail.com + dkim_signers = gmail.com + dkim_status = none +.endd + +.vitem &%dkim_status%& +ACL condition that checks a colon-separated list of possible DKIM verification +results agains the actual result of verification. This is typically used +to restrict an ACL verb to a list of verification outcomes, like: + +.code +deny message = Message from Paypal with invalid or missing signature + sender_domains = paypal.com:paypal.de + dkim_signers = paypal.com:paypal.de + dkim_status = none:invalid:fail +.endd + +The possible status keywords are: 'none','invalid','fail' and 'pass'. Please +see the documentation of the &%$dkim_verify_status%& expansion variable above +for more information of what they mean. +.endlist + . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// -.chapter "Adding new drivers or lookup types" "CHID12" &&& +.chapter "Adding new drivers or lookup types" "CHID13" &&& "Adding drivers or lookups" .cindex "adding drivers" .cindex "new drivers, adding"