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📄 NAME

pcre_table — format of Postfix PCRE tables

🚀 Quick Reference

🎯 Use Case	⚙️ Command	📝 Description
🔍 Query a PCRE table	postmap -q "string" pcre:/etc/postfix/filename	Look up a string in a PCRE lookup table
📨 Test header patterns	postmap -hmq - pcre:/etc/postfix/filename <inputfile	Test header_checks(5) patterns
📄 Test body patterns	postmap -bmq - pcre:/etc/postfix/filename <inputfile	Test body_checks(5) patterns (Postfix 2.6+)
📋 List supported table types	postconf -m	Show all supported lookup table types
🛡️ SMTPD access control	/pattern/action	Match and apply action in smtpd access map
📧 Header filter	/^Subject: spam/ REJECT	Filter mail headers with PCRE patterns
📄 Body filter	/pattern/ REJECT	Filter mail body content with PCRE patterns

🔧 SYNOPSIS

postmap -q "string" pcre:/etc/postfix/filename

postmap -q - pcre:/etc/postfix/filename <inputfile

postmap -hmq - pcre:/etc/postfix/filename <inputfile

postmap -bmq - pcre:/etc/postfix/filename <inputfile

📝 DESCRIPTION

The Postfix mail system uses optional tables for address rewriting, mail routing, or access control. These tables are usually in dbm or db format.

Alternatively, lookup tables can be specified in Perl Compatible Regular Expression form. In this case, each input is compared against a list of patterns. When a match is found, the corresponding result is returned and the search is terminated.

To find out what types of lookup tables your Postfix system supports use the postconf -m command.

To test lookup tables, use the postmap -q command as described in the SYNOPSIS above. Use postmap -hmq - <file for header_checks(5) patterns, and postmap -bmq - <file for body_checks(5) (Postfix 2.6 and later).

🔄 COMPATIBILITY

With Postfix version 2.2 and earlier specify postmap -fq to query a table that contains case sensitive patterns. Patterns are case insensitive by default.

📋 TABLE FORMAT

The general form of a PCRE table is:

• /pattern/flags result

  When pattern matches the input string, use the corresponding result value.

• !/pattern/flags result

  When pattern does not match the input string, use the corresponding result value.

• if /pattern/flags

  endif

  If the input string matches /pattern/, then match that input string against the patterns between if and endif. The if..endif can nest.

  Note: do not prepend whitespace to patterns inside if..endif.

  This feature is available in Postfix 2.1 and later.

• if !/pattern/flags

  endif

  If the input string does not match /pattern/, then match that input string against the patterns between if and endif. The if..endif can nest.

  Note: do not prepend whitespace to patterns inside if..endif.

  This feature is available in Postfix 2.1 and later.

• blank lines and comments

  Empty lines and whitespace-only lines are ignored, as are lines whose first non-whitespace character is a #.

• multi-line text

  A logical line starts with non-whitespace text. A line that starts with whitespace continues a logical line.

Each pattern is a perl-like regular expression. The expression delimiter can be any non-alphanumerical character, except whitespace or characters that have special meaning (traditionally the forward slash is used). The regular expression can contain whitespace.

By default, matching is case-insensitive, and newlines are not treated as special characters. The behavior is controlled by flags, which are toggled by appending one or more of the following characters after the pattern:

• i (default: on) — Toggles the case sensitivity flag. By default, matching is case insensitive.
• m (default: off) — Toggles the PCRE_MULTILINE flag. When this flag is on, the ^ and $ metacharacters match immediately after and immediately before a newline character, respectively, in addition to matching at the start and end of the subject string.
• s (default: on) — Toggles the PCRE_DOTALL flag. When this flag is on, the . metacharacter matches the newline character. With Postfix versions prior to 2.0, the flag is off by default, which is inconvenient for multi-line message header matching.
• x (default: off) — Toggles the pcre extended flag. When this flag is on, whitespace characters in the pattern (other than in a character class) are ignored. To include a whitespace character as part of the pattern, escape it with backslash.
  Note: do not use #comment after patterns.
• A (default: off) — Toggles the PCRE_ANCHORED flag. When this flag is on, the pattern is forced to be "anchored", that is, it is constrained to match only at the start of the string which is being searched (the "subject string"). This effect can also be achieved by appropriate constructs in the pattern itself.
• E (default: off) — Toggles the PCRE_DOLLAR_ENDONLY flag. When this flag is on, a $ metacharacter in the pattern matches only at the end of the subject string. Without this flag, a dollar also matches immediately before the final character if it is a newline character (but not before any other newline characters). This flag is ignored if PCRE_MULTILINE flag is set.
• U (default: off) — Toggles the ungreedy matching flag. When this flag is on, the pattern matching engine inverts the "greediness" of the quantifiers so that they are not greedy by default, but become greedy if followed by ?. This flag can also set by a (?U) modifier within the pattern.
• X (default: off) — Toggles the PCRE_EXTRA flag. When this flag is on, any backslash in a pattern that is followed by a letter that has no special meaning causes an error, thus reserving these combinations for future expansion.

🔍 SEARCH ORDER

Patterns are applied in the order as specified in the table, until a pattern is found that matches the input string.

Each pattern is applied to the entire input string. Depending on the application, that string is an entire client hostname, an entire client IP address, or an entire mail address. Thus, no parent domain or parent network search is done, and user@domain mail addresses are not broken up into their user and domain constituent parts, nor is user+foo broken up into user and foo.

🔤 TEXT SUBSTITUTION

Substitution of substrings (text that matches patterns inside ()) from the matched expression into the result string is requested with $1, $2, etc.; specify $$ to produce a $ character as output. The macros in the result string may need to be written as ${n} or $(n) if they aren't followed by whitespace.

Note: since negated patterns (those preceded by !) return a result when the expression does not match, substitutions are not available for negated patterns.

📧 EXAMPLE SMTPD ACCESS MAP

# Protect your outgoing majordomo exploders
/^(?!owner-)(.*)-outgoing@(.*)/ 550 Use ${1}@${2} instead

# Bounce friend@whatever, except when whatever is our domain (you would
# be better just bouncing all friend@ mail - this is just an example).
/^(friend@(?!my\.domain$).*)$/  550 Stick this in your pipe $1

# A multi-line entry. The text is sent as one line.
#
/^noddy@my\.domain$/
 550 This user is a funny one. You really don't want to send mail to
 them as it only makes their head spin.

📧 EXAMPLE HEADER FILTER MAP

/^Subject: make money fast/     REJECT
/^To: friend@public\.com/       REJECT

📧 EXAMPLE BODY FILTER MAP

# First skip over base 64 encoded text to save CPU cycles.
# Requires PCRE version 3.
~^[[:alnum:]+/]{60,}$~          OK

# Put your own body patterns here.

📚 SEE ALSO

• postmap(1), Postfix lookup table manager
• postconf(5), configuration parameters
• regexp_table(5), format of POSIX regular expression tables

📖 README FILES

Use postconf readme_directory or postconf html_directory to locate this information.

DATABASE_README, Postfix lookup table overview

👤 AUTHOR(S)

The PCRE table lookup code was originally written by:

• Andrew McNamara <andrewm AT connect.au>
  connect.com.au Pty. Ltd.
  Level 3, 213 Miller St
  North Sydney, NSW, Australia

Adopted and adapted by:

• Wietse Venema
  IBM T.J. Watson Research
  P.O. Box 704
  Yorktown Heights, NY 10598, USA
• Wietse Venema
  Google, Inc.
  111 8th Avenue
  New York, NY 10011, USA

📄 NAME 🚀 Quick Reference 🔧 SYNOPSIS 📝 DESCRIPTION 🔄 COMPATIBILITY 📋 TABLE FORMAT 🔍 SEARCH ORDER 🔤 TEXT SUBSTITUTION 📧 EXAMPLE SMTPD ACCESS MAP 📧 EXAMPLE HEADER FILTER MAP 📧 EXAMPLE BODY FILTER MAP 📚 SEE ALSO 📖 README FILES 👤 AUTHOR(S)