Substitute the contents of the named variable, for example

$local_part
${domain}

The second form can be used to separate the name from subsequent alphanumeric characters. This form (using braces) is available only for variables; it does not apply to message headers. The names of the variables are given in section 11.9 below. If the name of a non-existent variable is given, the expansion fails.

The string is first itself expanded, and then the operation specified by <op> is applied to it. For example,

${lc:$local_part}

The string starts with the first character after the colon, which may be leading white space. A list of operators is given in section 11.6 below. The operator notation is used for simple expansion items that have just one argument, because it reduces the number of braces and therefore makes the string easier to understand.

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 consist entirely of digits. The expanded <string1> must be of the form:

<key1> = <value1>  <key2> = <value2> ...

where the equals signs and spaces (but not both) are optional. If any of the values contain white space, they must be enclosed in double quotes, and any values that are enclosed in double quotes are subject to escape processing as described in section 6.16. The expanded <string1> is searched for the value that corresponds to the key. The search is case-insensitive. If the key is found, <string2> is expanded, and replaces the whole item; otherwise <string3> is used. During the expansion of <string2> the variable $value contains the value that has been extracted. Afterwards, it is restored to any previous value it might have had.

If {<string3>} is omitted, the item is replaced by an empty string if the key is not found. If {<string2>} is also omitted, the value that was extracted is used. Thus, for example, these two expansions are identical, and yield “2001”:

${extract{gid}{uid=1984 gid=2001}}
${extract{gid}{uid=1984 gid=2001}{$value}}

Instead of {<string3>} the word “fail” (not in curly brackets) can appear, for example:

${extract{Z}{A=... B=...}{$value} fail }

This forces an expansion failure (see section 11.4); {<string2>} must be present for “fail” to be recognized.

The <number> argument must consist entirely of decimal digits, apart from leading and trailing white space, which is ignored. This is what distinguishes this form of extract from the previous kind. It behaves in the same way, except that, instead of extracting a named field, it extracts from <string1> the field whose number is given as the first argument. You can use $value in <string2> or fail instead of <string3> as before.

The fields in the string are separated by any one of the characters in the separator string. These may include space or tab characters. The first field is numbered one. If the number is negative, the fields are counted from the end of the string, with the rightmost one numbered -1. If the number given is zero, the entire string is returned. If the modulus of the number is greater than the number of fields in the string, the result is the expansion of <string3>, or the empty string if <string3> is not provided. For example:

${extract{2}{:}{x:42:99:& Mailer::/bin/bash}}

yields “42”, and

${extract{-4}{:}{x:42:99:& Mailer::/bin/bash}}

yields “99”. Two successive separators mean that the field between them is empty (for example, the fifth field above).

This is a textual hashing function, and was the first to be implemented in early versions of Exim. In current releases, there are other hashing functions (numeric, MD5, and SHA-1), which are described below.

The first two strings, after expansion, must be numbers. Call them <m> and <n>. If you are using fixed values for these numbers, that is, if <string1> and <string2> do not change when they are expanded, you can use the simpler operator notation that avoids some of the braces:

${hash_<n>_<m>:<string>}

The second number is optional (in both notations).

If <n> is greater than or equal to the length of the string, the expansion item returns the string. Otherwise it computes a new string of length <n> by applying a hashing function to the string. The new string consists of characters taken from the first <m> characters of the string

abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQWRSTUVWXYZ0123456789

If <m> is not present the value 26 is used, so that only lower case letters appear. For example:

Substitute the contents of the named message header line, for example

$header_reply-to:

The newline that terminates a header line is not included in the expansion, but 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 data in the header line is interpreted.

In a filter file, the target character set for header can be specified by a command of the following form:

headers charset "UTF-8"

This command affects all references to $h_ (or $header_) expansions in subsequently obeyed filter commands. In the absence of this command, the target character set in a filter is taken from the setting of the headers_charset option in the runtime configuration. The value of this option defaults to the value of HEADERS_CHARSET in Local/Makefile. The ultimate default is ISO-8859-1.

Header names follow the syntax of RFC 2822, which states that they may contain any printing characters except space and colon. Consequently, curly brackets do not terminate header names, and should not be used to enclose them as if they were variables. Attempting to do so causes a syntax error.

Only header lines that are common to all copies of a message are visible to this mechanism. These are the original header lines that are received with the message, and any that are added by an ACL warn statement or by a system filter. Header lines that are added to a particular copy of a message by a router or transport are not accessible.

For incoming SMTP messages, no header lines are visible in ACLs that are obeyed before the DATA ACL, because the header structure is not set up until the message is received. Header lines that are added by warn statements in a RCPT ACL (for example) are saved until the message’s incoming header lines are available, at which point they are added. When a DATA ACL is running, however, header lines added by earlier ACLs are visible.

Upper case and lower case letters are synonymous in header names. If the following character is white space, the terminating colon may be omitted, but this is not recommended, because you may then forget it when it is needed. When white space terminates the header name, it is included in the expanded string. If the message does not contain the given header, the expansion item is replaced by an empty string. (See the def condition in section 11.7 for a means of testing for the existence of a header.)

If there is more than one header with the same name, they are all concatenated to form the substitution string, up to a maximum length of 64K. A newline character is inserted between each line. For the header expansion, for those headers that contain lists of addresses, a comma is also inserted at the junctions between lines. This does not happen for the rheader expansion.

This function uses cryptographic hashing (either MD5 or SHA-1) to convert a shared secret and some text into a message authentication code, as specified in RFC 2104. This differs from ${md5:secret_text…} or ${sha1:secret_text…} in that the hmac step adds a signature to the cryptographic hash, allowing for authentication that is not possible with MD5 or SHA-1 alone. The hash name must expand to either md5 or sha1 at present. For example:

${hmac{md5}{somesecret}{$primary_hostname $tod_log}}

For the hostname mail.example.com and time 2002-10-17 11:30:59, this produces:

dd97e3ba5d1a61b5006108f8c8252953

As an example of how this might be used, you might put in the main part of an Exim configuration:

SPAMSCAN_SECRET=cohgheeLei2thahw

In a router or a transport you could then have:

headers_add = \
  X-Spam-Scanned: ${primary_hostname} ${message_exim_id} \
  ${hmac{md5}{SPAMSCAN_SECRET}\
  {${primary_hostname},${message_exim_id},$h_message-id:}}

Then given a message, you can check where it was scanned by looking at the X-Spam-Scanned: header line. If you know the secret, you can check that this header line is authentic by recomputing the authentication code from the host name, message ID and the Message-id: header line. This can be done using Exim’s -be option, or by other means, for example by using the hmac_md5_hex() function in Perl.

If <condition> is true, <string1> is expanded and replaces the whole item; otherwise <string2> is used. The available conditions are described in section 11.7 below. For example:

${if eq {$local_part}{postmaster} {yes}{no} }

The second string need not be present; if it is not and the condition is not true, the item is replaced with nothing. Alternatively, the word “fail” may be present instead of the second string (without any curly brackets). In this case, the expansion is forced to fail if the condition is not true (see section 11.4).

If both strings are omitted, the result is the string true if the condition is true, and the empty string if the condition is false. This makes it less cumbersome to write custom ACL and router conditions. For example, instead of

condition = ${if >{$acl_m4}{3}{true}{false}}

you can use

condition = ${if >{$acl_m4}{3}}

The length item is used to extract the initial portion of a string. Both strings are expanded, and the first one must yield a number, <n>, say. If you are using a fixed value for the number, that is, if <string1> does not change when expanded, you can use the simpler operator notation that avoids some of the braces:

${length_<n>:<string>}

The result of this item is either the first <n> characters or the whole of <string2>, whichever is the shorter. Do not confuse length with strlen, which gives the length of a string.

The two forms of lookup item specify data lookups in files and databases, as discussed in chapter 9. The first form is used for single-key lookups, and the second is used for query-style lookups. The <key>, <file>, and <query> strings are expanded before use.

If there is any white space in a lookup item which is part of a filter command, a retry or rewrite rule, a routing rule for the manualroute router, or any other place where white space is significant, the lookup item must be enclosed in double quotes. The use of data lookups in users’ filter files may be locked out by the system administrator.

If the lookup succeeds, <string1> is expanded and replaces the entire item. During its expansion, the variable $value contains the data returned by the lookup. Afterwards it reverts to the value it had previously (at the outer level it is empty). If the lookup fails, <string2> is expanded and replaces the entire item. If {<string2>} is omitted, the replacement is the empty string on failure. If <string2> is provided, it can itself be a nested lookup, thus providing a mechanism for looking up a default value when the original lookup fails.

If a nested lookup is used as part of <string1>, $value contains the data for the outer lookup while the parameters of the second lookup are expanded, and also while <string2> of the second lookup is expanded, should the second lookup fail. + Instead of {<string2>} the word “fail” can appear, and in this case, if the lookup fails, the entire expansion is forced to fail (see section 11.4). If both {<string1>} and {<string2>} are omitted, the result is the looked up value in the case of a successful lookup, and nothing in the case of failure.

For single-key lookups, the string “partial” is permitted to precede the search type in order to do partial matching, and * or *@ may follow a search type to request default lookups if the key does not match (see sections 9.6 and 9.7 for details).

If a partial search is used, the variables $1 and $2 contain the wild and non-wild parts of the key during the expansion of the replacement text. They return to their previous values at the end of the lookup item.

This example looks up the postmaster alias in the conventional alias file:

${lookup {postmaster} lsearch {/etc/aliases} {$value}}

This example uses NIS+ to look up the full name of the user corresponding to the local part of an address, forcing the expansion to fail if it is not found:

${lookup nisplus {[name=$local_part],passwd.org_dir:gcos} \
  {$value}fail}

The three strings are expanded; the first two must yield numbers. Call them <n> and <m>. If you are using fixed values for these numbers, that is, if <string1> and <string2> do not change when they are expanded, you can use the simpler operator notation that avoids some of the braces:

${nhash_<n>_<m>:<string>}

The second number is optional (in both notations). If there is only one number, the result is a number in the range 0–<n>-1. Otherwise, the string is processed by a div/mod hash function that returns two numbers, separated by a slash, in the ranges 0 to <n>-1 and 0 to <m>-1, respectively. For example,

${nhash{8}{64}{supercalifragilisticexpialidocious}}

returns the string “6/33”.

This item is available only if Exim has been built to include an embedded Perl interpreter. The subroutine name and the arguments are first separately expanded, and then the Perl subroutine is called with those arguments. No additional arguments need be given; the maximum number permitted, including the name of the subroutine, is nine.

The return value of the subroutine is inserted into the expanded string, unless the return value is undef. In that case, the expansion fails in the same way as an explicit “fail” on a lookup item. The return value is a scalar. Whatever you return is evaluated in a scalar context. For example, if you return the name of a Perl vector, the return value is the size of the vector, not its contents.

If the subroutine exits by calling Perl’s die function, the expansion fails with the error message that was passed to die. More details of the embedded Perl facility are given in chapter 12.

The redirect router has an option called forbid_filter_perl which locks out the use of this expansion item in filter files.

The file name and end-of-line string are first expanded separately. The file is then read, and its contents replace the entire item. All newline characters in the file are replaced by the end-of-line string if it is present. Otherwise, newlines are left in the string. String expansion is not applied to the contents of the file. If you want this, you must wrap the item in an expand operator. If the file cannot be read, the string expansion fails.

The redirect router has an option called forbid_filter_readfile which locks out the use of this expansion item in filter files.

This item inserts data that is read from a Unix domain socket into the expanded string. The minimal way of using it uses just two arguments:

${readsocket{/socket/name}{request string}}

Exim connects to the socket, writes the request string (unless it is an empty string) and reads from the socket until an end-of-file is read. A timeout of 5 seconds is applied. Additional, optional arguments extend what can be done. Firstly, you can vary the timeout. For example:

${readsocket{/socket/name}{request-string}{3s}}

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:

${readsocket{/socket/name}{request-string}{3s}{ }}

As with all expansions, the substrings are expanded before the processing happens. Errors in these sub-expansions cause the expansion to fail. In addition, the following errors can occur:

By default, any of these errors causes the expansion to fail. However, if you supply a fifth substring, it is expanded and used when any of the above errors occurs. For example:

  ${readsocket{/socket/name}{request-string}{3s}{\n}\
    {socket failure}}

You can test for the existence of the socket by wrapping this expansion in ${if exists, but there is a race condition between that test and the actual opening of the socket, so it is safer to use the fifth argument if you want to be absolutely sure of avoiding an expansion error for a non-existent socket.

The redirect router has an option called forbid_filter_readsocket which locks out the use of this expansion item in filter files.

The command and its arguments are first expanded separately, and then the command is run in a separate process, but under the same uid and gid. As in other command executions from Exim, a shell is not used by default. If you want a shell, you must explicitly code it.

The return code from the command is put in the variable $runrc, and this remains set afterwards, so in a filter file you can do things like this:

if "${run{x y z}{}}$runrc" is 1 then ...
  elif $runrc is 2 then ...
  ...
endif

If execution of the command fails (for example, the command does not exist), the return code is 127 – the same code that shells use for non-existent commands.

Warning: In a router or transport, you cannot assume the order in which option values are expanded, except for those pre-conditions whose order of testing is documented. Therefore, you cannot reliably expect to set $runrc by the expansion of one option, and use it in another.

The redirect router has an option called forbid_filter_run which locks out the use of this expansion item in filter files.

This item works like Perl’s substitution operator (s) with the global (/g) option; hence its name. However, unlike the Perl equivalent, Exim does not modify the subject string; instead it returns the modified string for insertion into the overall expansion. The item takes three arguments: the subject string, a regular expression, and a substitution string. For example

${sg{abcdefabcdef}{abc}{xyz}}

yields “xyzdefxyzdef”. Because all three arguments are expanded before use, if any $ or \ characters are required in the regular expression or in the substitution string, they have to be escaped. For example

${sg{abcdef}{^(...)(...)\$}{\$2\$1}}

yields “defabc”, and

${sg{1=A 4=D 3=C}{\N(\d+)=\N}{K\$1=}}

yields “K1=A K4=D K3=C”. Note the use of \N to protect the contents of the regular expression from string expansion.

The three strings are expanded; the first two must yield numbers. Call them <n> and <m>. If you are using fixed values for these numbers, that is, if <string1> and <string2> do not change when they are expanded, you can use the simpler operator notation that avoids some of the braces:

${substr_<n>_<m>:<string>}

The second number is optional (in both notations). If it is absent in the simpler format, the preceding underscore must also be omitted.

The substr item can be used to extract more general substrings than length. The first number, <n>, is a starting offset, and <m> is the length required. For example

${substr{3}{2}{$local_part}}

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.

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,

${substr{-5}{2}{1234567}}

yields “34”. If the absolute value of a negative offset is greater than the length of the string, the substring starts at the beginning of the string, and the length is reduced by the amount of overshoot. Thus, for example,

${substr{-5}{2}{12}}

yields an empty string, but

${substr{-3}{2}{12}}

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 string preceding the offset point are taken. For example, an offset of -1 and no length, as in these semantically identical examples:

${substr_-1:abcde}
${substr{-1}{abcde}}

yields all but the last character of the string, that is, “abcd”.

This item does single-character 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

${tr{abcdea}{ac}{13}}

yields 1b3de1. If there are duplicates in the second character string, the 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.

For eval, numbers may be decimal, octal (starting with “0”) or hexadecimal (starting with “0x”). For eval10, all numbers are taken as decimal, even if they start with a leading zero. This can be useful when processing numbers extracted from dates or times, which often do have leading zeros.

A number may be followed by “K” or “M” to multiply it by 1024 or 1024*1024, respectively. Negative numbers are supported. The result of the computation is a decimal representation of the answer (without “K” or “M”). For example:

As a more realistic example, in an ACL you might have

deny   message = Too many bad recipients
       condition =                    \
         ${if and {                   \
           {>{$rcpt_count}{10}}       \
           {                          \
           <                          \
             {$recipients_count}      \
             {${eval:$rcpt_count/2}}  \
           }                          \
         }{yes}{no}}

The condition is true if there have been more than 10 RCPT commands and fewer than half of them have resulted in a valid recipient.

The expand operator causes a string to be expanded for a second time. For example,

${expand:${lookup{$domain}dbm{/some/file}{$value}}}

first looks up a string in a file while expanding the operand for expand, and then re-expands what it has found.

The world is slowly moving towards Unicode, although there are no standards for email yet. However, other applications (including some databases) are starting to store data in Unicode, using UTF-8 encoding. This operator converts from a UTF-8 string to an ISO-8859-1 string. UTF-8 code values greater than 255 are converted to underscores. The input must be a valid UTF-8 string. If it is not, the result is an undefined sequence of bytes.

Unicode code points with values less than 256 are compatible with ASCII and ISO-8859-1 (also known as Latin-1). For example, character 169 is the copyright symbol in both cases, though the way it is encoded is different. In UTF-8, more than one byte is needed for characters with code values greater than 127, whereas ISO-8859-1 is a single-byte encoding (but thereby limited to 256 characters). This makes translation from UTF-8 to ISO-8859-1 straightforward.

The hash operator is a simpler interface to the hashing function that can be used when the two parameters are fixed numbers (as opposed to strings that change when expanded). The effect is the same as

${hash{<n>}{<m>}{<string>}}

See the description of the general hash item above for details. The abbreviation h can be used when hash is used as an operator.

This forces the letters in the string into lower-case, for example:

${lc:$local_part}

The length operator is a simpler interface to the length function that can be used when the parameter is a fixed number (as opposed to a string that changes when expanded). The effect is the same as

${length{<number>}{<string>}}

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.

If the form of the string to be operated on is not an IP address followed by a slash and an integer (that is, a network address in CIDR notation), the expansion fails. Otherwise, this operator converts the IP address to binary, masks off the least significant bits according to the bit count, and converts the result back to text, with mask appended. For example,

${mask:10.111.131.206/28}

returns the string “10.111.131.192/28”. Since this operation is expected to be mostly used for looking up masked addresses in files, the result for an IPv6 address uses dots to separate components instead of colons, because colon terminates a key string in lsearch files. So, for example,

${mask:3ffe:ffff:836f:0a00:000a:0800:200a:c031/99}

returns the string

3ffe.ffff.836f.0a00.000a.0800.2000.0000/99

Letters in IPv6 addresses are always output in lower case.

The nhash operator is a simpler interface to the numeric hashing function that can be used when the two parameters are fixed numbers (as opposed to strings that change when expanded). The effect is the same as

${nhash{<n>}{<m>}{<string>}}

See the description of the general nhash item above for details.

The quote operator puts its argument into double quotes if it is an empty string or contains anything other than letters, digits, underscores, dots, and hyphens. Any occurrences of double quotes and backslashes are escaped with a backslash. Newlines and carriage returns are converted to \n and \r, respectively For example,

${quote:ab"*"cd}

becomes

"ab\"*\"cd"

The place where this is useful is when the argument is a substitution from a variable or a message header.

This operator applies lookup-specific quoting rules to the string. Each query-style lookup type has its own quoting rules which are described with the lookups in chapter 9. For example,

${quote_ldap:two * two}

returns

two%20%5C2A%20two

For single-key lookup types, no quoting is ever necessary and this operator yields an unchanged string.

This operator encodes text according to the rules of RFC 2047. This is an encoding that is used in header lines to encode non-ASCII characters. It is assumed that the input string is in the encoding specified by the headers_charset option, which defaults to ISO-8859-1. If the string contains only characters in the range 33–126, and no instances of the characters

? = ( ) < > @ , ; : \ " . [ ] _

it is not modified. Otherwise, the result is the RFC 2047 encoding of the string, using as many “encoded words” as necessary to encode all the characters.

The string, after expansion, must be a file path. A call to the stat() function is made for this path. If stat() fails, an error occurs and the expansion fails. If it succeeds, the data from the stat replaces the item, as a series of <name>=<value> pairs, where the values are all numerical, except for the value of “smode”. The names are: “mode” (giving the mode as a 4-digit octal number), “smode” (giving the mode in symbolic format as a 10-character string, as for the ls command), “inode”, “device”, “links”, “uid”, “gid”, “size”, “atime”, “mtime”, and “ctime”. You can extract individual fields using the extract expansion item.

The substr operator is a simpler interface to the substr function that can be used when the two parameters are fixed numbers (as opposed to strings that change when expanded). The effect is the same as

${substr{<start>}{<length>}{<string>}}

See the description of the general substr item above for details. The abbreviation s can be used when substr is used as an operator.

There are a number of symbolic operators for doing numeric comparisons. They are:

For example,

${if >{$message_size}{10M} ...

Note that the general negation operator provides for inequality testing. The two strings must take the form of optionally signed decimal integers, optionally followed by one of the letters “K” or “M” (in either upper or lower case), signifying multiplication by 1024 or 1024*1024, respectively.

This condition is included in the Exim binary if it is built to support any authentication mechanisms (see chapter 33). Otherwise, it is necessary to define SUPPORT_CRYPTEQ in Local/Makefile to get crypteq included in the binary.

The crypteq condition has two arguments. The first is encrypted and compared against the second, which is already encrypted. The second string may be in the LDAP form for storing encrypted strings, which starts with the encryption type in curly brackets, followed by the data. If the second string does not begin with “{” it is assumed to be encrypted with crypt() or crypt16() (see below), since such strings cannot begin with “{”. Typically this will be a field from a password file.

An example of an encrypted string in LDAP form is:

{md5}CY9rzUYh03PK3k6DJie09g==

If such a string appears directly in an expansion, the curly brackets have to be quoted, because they are part of the expansion syntax. For example:

${if crypteq {test}{\{md5\}CY9rzUYh03PK3k6DJie09g==}{yes}{no}}

The following encryption types (whose names are matched case-independently) are supported:

Exim has its own version of crypt16() (which is just a double call to crypt()). For operating systems that have their own version, setting HAVE_CRYPT16 in Local/Makefile when building Exim causes it to use the operating system version instead of its own. This option is set by default in the OS-dependent Makefile for those operating systems that are known to support crypt16().

If you do not put any curly bracket encryption type in a crypteq comparison, the default is either {crypt} or {crypt16}, as determined by the setting of DEFAULT_CRYPT in Local/Makefile. The default default is {crypt}. Whatever the default, you can always use either function by specifying it explicitly in curly brackets.

Note that if a password is no longer than 8 characters, the results of encrypting it with crypt() and crypt16() are identical. That means that crypt16() is backwards compatible, as long as nobody feeds it a password longer than 8 characters.

The def condition must be followed by the name of one of the expansion variables defined in section 11.9. The condition is true if the named expansion variable does not contain the empty string, for example

${if def:sender_ident {from $sender_ident}}

Note that the variable name is given without a leading $ character. If the variable does not exist, the expansion fails.

This condition is true if a message is being processed and the named header exists in the message. For example,

${if def:header_reply-to:{$h_reply-to:}{$h_from:}}

Note: no $ appears before header_ or h_ in the condition, and the header name must be terminated by a colon if white space does not follow.

The substring is first expanded, and then tested to see if it has the form of an IP address. Both IPv4 and IPv6 addresses are valid for isip, whereas isip4 and isip6 test just for IPv4 or IPv6 addresses, respectively. For example, you could use

${if isip4{$sender_host_address}...

to test which version of IP an incoming SMTP connection is using.

The two substrings are first expanded. The second is then treated as a regular expression and applied to the first. Because of the pre-expansion, if the regular expression contains dollar, or backslash characters, they must be escaped. Care must also be taken if the regular expression contains braces (curly brackets). A closing brace must be escaped so that it is not taken as a premature termination of <string2>. The easiest approach is to use the \N feature to disable expansion of the regular expression. For example,

${if match {$local_part}{\N^\d{3}\N} ...

If the whole expansion string is in double quotes, further escaping of backslashes is also required.

The condition is true if the regular expression match succeeds. The regular expression is not required to begin with a circumflex metacharacter, but if there is no circumflex, the expression is not anchored, 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.

At the start of an if expansion the values of the numeric variable substitutions $1 etc. are remembered. Obeying a match condition that succeeds causes them to be reset to the substrings of that condition and they will have these values during the expansion of the success string. At the end of the if expansion, the previous values are restored. After testing a combination of conditions using or, the subsequent values of the numeric variables are those of the condition that succeeded.

This condition, together with match_address and match_domain, make it possible to test domain, address, and local part lists within expansions. Each condition requires two arguments: an item and a list to match. A trivial example is:

${if match_domain{a.b.c}{x.y.z:a.b.c:p.q.r}{yes}{no}}

In each case, the second argument may contain any of the allowable items for a list of the appropriate type. Also, because the second argument (after expansion) is a standard form of list, it is possible to refer to a named list. Thus, you can use conditions like this:

${if match_domain{$domain}{+local_domains}{...

For address lists, the matching starts off caselessly, but the +caseful item can be used, as in all address lists, to cause subsequent items to have their local parts matched casefully. Domains are always matched caselessly.

Note: Host lists are not supported in this way. This is because hosts have two identities: a name and an IP address, and it is not clear how to specify cleanly how such a test would work. However, IP addresses can be matched using match_ip.

Pluggable Authentication Modules (http://www.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

SUPPORT_PAM=yes

in Local/Makefile. You probably need to add -lpam to EXTRALIBS, and in some releases of GNU/Linux -ldl is also needed.

The argument string is first expanded, and the result must be a colon-separated list of strings. Leading and trailing white space is ignored. The PAM module is initialized with the service name “exim” and the user name taken from the first item in the colon-separated data string (<string1>). The remaining items in the data string are passed over in response to requests from the authentication function. In the simple case there will only be one request, for a password, so the data consists of just two strings.

There can be problems if any of the strings are permitted to contain colon characters. In the usual way, these have to be doubled to avoid being taken as separators. If the data is being inserted from a variable, the sg expansion item can be used to double any existing colons. For example, the configuration of a LOGIN authenticator might contain this setting:

server_condition = ${if pam{$1:${sg{$2}{:}{::}}}{yes}{no}}

For a PLAIN authenticator you could use:

server_condition = ${if pam{$2:${sg{$3}{:}{::}}}{yes}{no}}

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 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.

This condition supports user authentication using the Cyrus pwcheck daemon. This is one way of making it possible for passwords to be checked by a process that is not running as root. Note: The use of pwcheck is now deprecated. Its replacement is saslauthd (see below).

The pwcheck support is not included in Exim by default. You need to specify the location of the pwcheck daemon’s socket in Local/Makefile before building Exim. For example:

CYRUS_PWCHECK_SOCKET=/var/pwcheck/pwcheck

You do not need to install the full Cyrus software suite in order to use the pwcheck daemon. You can compile and install just the daemon alone from the Cyrus SASL library. Ensure that exim is the only user that has access to the /var/pwcheck directory.

The pwcheck condition takes one argument, which must be the user name and password, separated by a colon. For example, in a LOGIN authenticator configuration, you might have this:

server_condition = ${if pwcheck{$1:$2}{1}{0}}

Radius authentication (RFC 2865) is supported in a similar way to PAM. You must set RADIUS_CONFIG_FILE in Local/Makefile to specify the location of the Radius client configuration file in order to build Exim with Radius support.

RADIUS_LIB_TYPE=RADIUSCLIENTNEW

RADIUS_LIB_TYPE=RADLIB

in Local/Makefile, in addition to setting RADIUS_CONFIGURE_FILE. You may also have to supply a suitable setting in EXTRALIBS so that the Radius library can be found when Exim is linked.

The string specified by RADIUS_CONFIG_FILE is expanded and passed to the Radius client library, which calls the Radius server. The condition is true if the authentication is successful. For example

server_condition = \$\{if radius\{<arguments>\}\{yes\}\{no\}\}

This condition supports user authentication using the Cyrus saslauthd daemon. This replaces the older pwcheck daemon, which is now deprecated. Using this daemon is one way of making it possible for passwords to be checked by a process that is not running as root.

The saslauthd support is not included in Exim by default. You need to specify the location of the saslauthd daemon’s socket in Local/Makefile before building Exim. For example:

CYRUS_SASLAUTHD_SOCKET=/var/state/saslauthd/mux

You do not need to install the full Cyrus software suite in order to use the saslauthd daemon. You can compile and install just the daemon alone from the Cyrus SASL library.

Up to four arguments can be supplied to the saslauthd condition, but only two are mandatory. For example:

server_condition = ${if saslauthd{{$1}{$2}}{1}{0}}

The service and the realm are optional (which is why the arguments are enclosed in their own set of braces). For details of the meaning of the service and realm, and how to run the daemon, consult the Cyrus documentation.

The sub-conditions are evaluated from left to right. The condition is true if any one of the sub-conditions is true. For example,

${if or {{eq{$local_part}{spqr}}{eq{$domain}{testing.com}}}...

When a true sub-condition is found, the following ones are parsed but not evaluated. If there are several “match” sub-conditions the values of the numeric variables afterwards are taken from the first one that succeeds.

This variable is set by means of the address_data option in routers. The value then remains with the address while it is processed by subsequent routers and eventually a transport. If the transport is handling multiple addresses, the value from the first address is used. See chapter 15 for more details. Note: the contents of $address_data are visible in user filter files.

If $address_data is set when the routers are called from an ACL to verify a recipient address, the final value is still in the variable for subsequent conditions and modifiers of the ACL statement. If routing the address caused it to be redirected to just one address, the child address is also routed as part of the verification, and in this case the final value of $address_data is from the child’s routing.

If $address_data is set when the routers are called from an ACL to verify a sender address, the final value is also preserved, but this time in $sender_address_data, to distinguish it from data from a recipient address.

In both cases (recipient and sender verification), the value does not persist after the end of the current ACL statement. If you want to preserve these values for longer, you can save them in ACL variables.

When, as a result of aliasing, forwarding, or filtering, a message is directed to a specific file, this variable holds the name of the file when the transport is running. At other times, the variable is empty. For example, using the default configuration, if user r2d2 has a .forward file containing

/home/r2d2/savemail

then when the address_file transport is running, $address_file contains “/home/r2d2/savemail”.

For Sieve filters, the value may be “inbox” or a relative folder name. It is then up to the transport configuration to generate an appropriate absolute path to the relevant file.

When acting as a server, Exim takes note of the AUTH= parameter on an incoming SMTP MAIL command if it believes the sender is sufficiently trusted, as described in section 33.2. Unless the data is the string “<>”, it is set as the authenticated sender of the message, and the value is available during delivery in the $authenticated_sender variable. If the sender is not trusted, Exim accepts the syntax of AUTH=, but ignores the data.

When a message is submitted locally (that is, not over a TCP connection), the value of $authenticated_sender is an address constructed from the login name of the calling process and $qualify_domain.

When an address is being routed, or delivered on its own, this variable contains the domain. Global address rewriting happens when a message is received, so the value of $domain during routing and delivery is the value after rewriting. $domain is set during user filtering, but not during system filtering, because a message may have many recipients and the system filter is called just once.

When more than one address is being delivered at once (for example, several RCPT commands in one SMTP delivery), $domain is set only if they all have the same domain. Transports can be restricted to handling only one domain at a time if the value of $domain is required at transport time – this is the default for local transports. For further details of the environment in which local transports are run, see chapter 23.

At the end of a delivery, if all deferred addresses have the same domain, it is set in $domain during the expansion of delay_warning_condition.

The $domain variable is also used in some other circumstances:

When the domains option on a router matches a domain by means of a lookup, the data read by the lookup is available during the running of the router as $domain_data. In addition, if the driver routes the address to a transport, the value is available in that transport. If the transport is handling multiple addresses, the value from the first address is used.

$domain_data is also set when the domains condition in an ACL matches a domain by means of a lookup. The data read by the lookup is available during the rest of the ACL statement. In all other situations, this variable expands to nothing.

When the check_local_user option is set for a router, the user’s home directory is placed in $home when the check succeeds. In particular, this means it is set during the running of users’ filter files. A router may also explicitly set a home directory for use by a transport; this can be overridden by a setting on the transport itself.

When running a filter test via the -bf option, $home is set to the value of the environment variable HOME.

When the smtp transport is expanding its options for encryption using TLS, $host contains the name of the host to which it is connected. Likewise, when used in the client part of an authenticator configuration (see chapter 33), $host contains the name of the server to which the client is connected.

When used in a transport filter (see chapter 24) $host refers to the host involved in the current connection. When a local transport is run as a result of a router that sets up a host list, $host contains the name of the first host.

If a hosts condition in an ACL is satisfied by means of a lookup, the result of the lookup is made available in the $host_data variable. This allows you, for example, to do things like this:

deny  hosts = net-lsearch;/some/file
      message = $host_data

This variable normally contains “0”, as does $host_lookup_failed. When a message comes from a remote host and there is an attempt to look up the host’s name from its IP address, and the attempt is not successful, one of these variables is set to “1”.

Looking up a host’s name from its IP address consists of more than just a single reverse lookup. Exim checks that a forward lookup of at least one of the names it receives from a reverse lookup yields the original IP address. If this is not the case, Exim does not accept the looked up name(s), and $host_lookup_failed is set to “1”. Thus, being able to find a name from an IP address (for example, the existence of a PTR record in the DNS) is not sufficient on its own for the success of a host name lookup. If the reverse lookup succeeds, but there is a lookup problem such as a timeout when checking the result, the name is not accepted, and $host_lookup_deferred is set to “1”. See also $sender_host_name.

When an address is being routed, or delivered on its own, this variable contains the local part. When a number of addresses are being delivered together (for example, multiple RCPT commands in an SMTP session), $local_part is not set.

Global address rewriting happens when a message is received, so the value of $local_part during routing and delivery is the value after rewriting. $local_part is set during user filtering, but not during system filtering, because a message may have many recipients and the system filter is called just once.

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 $local_part_suffix, respectively.

When a message is being delivered to a file, pipe, or autoreply transport as a result of aliasing or forwarding, $local_part is set to the local part of the parent address, not to the file name or command (see $address_file and $address_pipe).

When an ACL is running for a RCPT command, $local_part contains the local part of the recipient address.

When a rewrite item is being processed (see chapter 31), $local_part contains the local part of the address that is being rewritten; it can be used in the expansion of the replacement address, for example.

In all cases, all quoting is removed from the local part. For example, for both the addresses

"abc:xyz"@test.example
abc\:xyz@test.example

the value of $local_part is

abc:xyz

If you use $local_part to create another address, you should always wrap it inside a quoting operator. For example, in a redirect router you could have:

data = ${quote_local_part:$local_part}@new.domain.example

Note: The value of $local_part is normally lower cased. If you want to process local parts in a case-dependent manner in a router, you can set the caseful_local_part option (see chapter 15).

When the local_parts option on a router matches a local part by means of a lookup, the data read by the lookup is available during the running of the router as $local_part_data. In addition, if the driver routes the address to a transport, the value is available in that transport. If the transport is handling multiple addresses, the value from the first address is used.

$local_part_data is also set when the local_parts condition in an ACL matches a local part by means of a lookup. The data read by the lookup is available during the rest of the ACL statement. In all other situations, this variable expands to nothing.

When a message is being processed, this variable contains its size in bytes. In most cases, the size includes those headers that were received with the message, but not those (such as Envelope-to:) that are added to individual deliveries as they are written. However, there is one special case: during the expansion of the maildir_tag option in the appendfile transport while doing a delivery in maildir format, the value of $message_size is the precise size of the file that has been written. See also $message_body_size, $body_linecount, and $body_zerocount.

While running an ACL at the time of an SMTP RCPT command, $message_size contains the size supplied on the MAIL command, or -1 if no size was given. The value may not, of course, be truthful.

When a top-level address is being processed for delivery, this contains the same value as $domain. However, if a “child” address (for example, generated by an alias, forward, or filter file) is being processed, this variable contains the domain of the original address. This differs from $parent_domain only when there is more than one level of aliasing or forwarding. When more than one address is being delivered in a single transport run, $original_domain is not set.

If new an address is created by means of a deliver command in a system filter, it is set up with an artificial “parent” address. This has the local part system-filter and the default qualify domain.

When a top-level address is being processed for delivery, this contains the same value as $local_part, unless a prefix or suffix was removed from the local part, because $original_local_part always contains the full local part. When a “child” address (for example, generated by an alias, forward, or filter file) is being processed, this variable contains the full local part of the original address.

If the router that did the redirection processed the local part case-insensitively, the value in $original_local_part is in lower case. This variable differs from $parent_local_part only when there is more than one level of aliasing or forwarding. When more than one address is being delivered in a single transport run, $original_local_part is not set.

If new an address is created by means of a deliver command in a system filter, it is set up with an artificial “parent” address. This has the local part system-filter and the default qualify domain.

When a message is being processed, this variable contains the name of the protocol by which it was received. Most of the names used by Exim are defined by RFCs 821, 2821, and 3848. They start with “smtp” (the client used HELO) or “esmtp” (the client used EHLO). This can be followed by “s” for secure (encrypted) and/or “a” for authenticated. Thus, for example, if the protocol is set to “esmtpsa”, the message was received over an encrypted SMTP connection and the client was successfully authenticated.

Exim uses the protocol name “smtps” for the case when encryption is automatically set up on connection without the use of STARTTLS (see tls_on_connect_ports), and the client uses HELO to initiate the encrypted SMTP session. The name “smtps” is also used for the rare situation where the client initially uses EHLO, sets up an encrypted connection using STARTTLS, and then uses HELO afterwards.

The -oMr option provides a way of specifying a custom protocol name for messages that are injected locally by trusted callers. This is commonly used to identify messages that are being re-injected after some kind of scanning.

This variable is set after an indexing lookup success in an ACL recipients condition. It contains the data from the lookup, and the value remains set until the next recipients test. Thus, you can do things like this:

Warning: This variable is set only when a lookup is used as an indexing method in the address list, using the semicolon syntax as in the example above. The variable is not set for a lookup that is used as part of the string expansion that all such lists undergo before being interpreted.

In an ACL, when a recipient verification fails, this variable contains information about the failure. It is set to one of the following words:

The main use of this variable is expected to be to distinguish between rejections of MAIL and rejections of RCPT.

This variable contains a list of envelope recipients for a message. A comma and a space separate the addresses in the replacement text. However, the variable is not generally available, to prevent exposure of Bcc recipients in unprivileged users’ filter files. You can use $recipients only in these two cases:

This variable is set after a lookup success in an ACL senders condition or in a router senders option. It contains the data from the lookup, and the value remains set until the next senders test. Thus, you can do things like this:

Warning: This variable is set only when a lookup is used as an indexing method in the address list, using the semicolon syntax as in the example above. The variable is not set for a lookup that is used as part of the string expansion that all such lists undergo before being interpreted.

When a message is received from a remote host, this variable contains the host’s name as obtained by looking up its IP address. For messages received by other means, this variable is empty.

If the host name has not previously been looked up, a reference to $sender_host_name triggers a lookup (for messages from remote hosts). A looked up name is accepted only if it leads back to the original IP address via a forward lookup. If either the reverse or the forward lookup fails to find any data, or if the forward lookup does not yield the original IP address, $sender_host_name remains empty, and $host_lookup_failed is set to “1”.

However, if either of the lookups cannot be completed (for example, there is a DNS timeout), $host_lookup_deferred is set to “1”, and $host_lookup_failed remains set to “0”.

Once $host_lookup_failed is set to “1”, Exim does not try to look up the host name again if there is a subsequent reference to $sender_host_name in the same Exim process, but it does try again if $sender_host_deferred is set to “1”.

Exim does not automatically look up every calling host’s name. If you want maximum efficiency, you should arrange your configuration so that it avoids these lookups altogether. The lookup happens only if one or more of the following are true:

This is provided specifically for use in Received: headers. It starts with either the verified host name (as obtained from a reverse DNS lookup) or, if there is no verified host name, the IP address in square brackets. After that there may be text in parentheses. When the first item is a verified host name, the first thing in the parentheses is the IP address in square brackets, followed by a colon and a port number if port logging is enabled. When the first item is an IP address, the port is recorded as “port=xxxx” inside the parentheses.

There may also be items of the form “helo=xxxx” if HELO or EHLO was used and its argument was not identical to the real host name or IP address, and “ident=xxxx” if an RFC 1413 ident string is available. If all three items are present in the parentheses, a newline and tab are inserted into the string, to improve the formatting of the Received: header.

MAIL FROM:<>
MAIL FROM: <>

For a MAIL command, extra parameters such as SIZE can be inspected. For a RCPT command, the address in $smtp_command is the original address before any rewriting, whereas the values in $local_part and $domain are taken from the address after SMTP-time rewriting.

The amount of free space (as a number of kilobytes) in the disk partition where Exim’s spool files are being written. The value is recalculated whenever the variable is referenced. If the operating system does not have the ability to find the amount of free space (only true for experimental systems), the space value is -1. For example, to check in an ACL that there is at least 50 megabytes free on the spool, you could write:

condition = ${if > {$spool_space}{50000}}

See also the check_spool_space option.