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550 lines
23 KiB
550 lines
23 KiB
# HEADER_CHECKS(5) HEADER_CHECKS(5)
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#
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# NAME
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# header_checks - Postfix built-in content inspection
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#
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# SYNOPSIS
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# header_checks = pcre:/etc/postfix/header_checks
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# mime_header_checks = pcre:/etc/postfix/mime_header_checks
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# nested_header_checks = pcre:/etc/postfix/nested_header_checks
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# body_checks = pcre:/etc/postfix/body_checks
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#
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# milter_header_checks = pcre:/etc/postfix/milter_header_checks
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#
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# smtp_header_checks = pcre:/etc/postfix/smtp_header_checks
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# smtp_mime_header_checks = pcre:/etc/postfix/smtp_mime_header_checks
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# smtp_nested_header_checks = pcre:/etc/postfix/smtp_nested_header_checks
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# smtp_body_checks = pcre:/etc/postfix/smtp_body_checks
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#
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# postmap -q "string" pcre:/etc/postfix/filename
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# postmap -q - pcre:/etc/postfix/filename <inputfile
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#
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# DESCRIPTION
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# This document describes access control on the content of
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# message headers and message body lines; it is implemented
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# by the Postfix cleanup(8) server before mail is queued.
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# See access(5) for access control on remote SMTP client
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# information.
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#
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# Each message header or message body line is compared
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# against a list of patterns. When a match is found the
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# corresponding action is executed, and the matching process
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# is repeated for the next message header or message body
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# line.
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#
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# Note: message headers are examined one logical header at a
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# time, even when a message header spans multiple lines.
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# Body lines are always examined one line at a time.
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#
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# For examples, see the EXAMPLES section at the end of this
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# manual page.
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#
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# Postfix header or body_checks are designed to stop a flood
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# of mail from worms or viruses; they do not decode attach-
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# ments, and they do not unzip archives. See the documents
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# referenced below in the README FILES section if you need
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# more sophisticated content analysis.
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#
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# FILTERS WHILE RECEIVING MAIL
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# Postfix implements the following four built-in content
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# inspection classes while receiving mail:
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#
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# header_checks (default: empty)
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# These are applied to initial message headers
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# (except for the headers that are processed with
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# mime_header_checks).
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#
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# mime_header_checks (default: $header_checks)
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# These are applied to MIME related message headers
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# only.
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#
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# This feature is available in Postfix 2.0 and later.
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#
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# nested_header_checks (default: $header_checks)
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# These are applied to message headers of attached
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# email messages (except for the headers that are
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# processed with mime_header_checks).
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#
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# This feature is available in Postfix 2.0 and later.
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#
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# body_checks
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# These are applied to all other content, including
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# multi-part message boundaries.
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#
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# With Postfix versions before 2.0, all content after
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# the initial message headers is treated as body con-
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# tent.
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#
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# FILTERS AFTER RECEIVING MAIL
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# Postfix supports a subset of the built-in content inspec-
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# tion classes after the message is received:
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#
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# milter_header_checks (default: empty)
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# These are applied to headers that are added with
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# Milter applications.
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#
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# This feature is available in Postfix 2.7 and later.
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#
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# FILTERS WHILE DELIVERING MAIL
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# Postfix supports all four content inspection classes while
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# delivering mail via SMTP.
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#
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# smtp_header_checks (default: empty)
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#
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# smtp_mime_header_checks (default: empty)
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#
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# smtp_nested_header_checks (default: empty)
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#
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# smtp_body_checks (default: empty)
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# These features are available in Postfix 2.5 and
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# later.
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#
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# COMPATIBILITY
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# With Postfix version 2.2 and earlier specify "postmap -fq"
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# to query a table that contains case sensitive patterns. By
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# default, regexp: and pcre: patterns are case insensitive.
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#
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# TABLE FORMAT
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# This document assumes that header and body_checks rules
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# are specified in the form of Postfix regular expression
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# lookup tables. Usually the best performance is obtained
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# with pcre (Perl Compatible Regular Expression) tables. The
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# regexp (POSIX regular expressions) tables are usually
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# slower, but more widely available. Use the command "post-
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# conf -m" to find out what lookup table types your Postfix
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# system supports.
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#
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# The general format of Postfix regular expression tables is
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# given below. For a discussion of specific pattern or
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# flags syntax, see pcre_table(5) or regexp_table(5),
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# respectively.
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#
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# /pattern/flags action
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# When /pattern/ matches the input string, execute
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# the corresponding action. See below for a list of
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# possible actions.
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#
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# !/pattern/flags action
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# When /pattern/ does not match the input string,
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# execute the corresponding action.
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#
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# if /pattern/flags
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#
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# endif If the input string matches /pattern/, then match
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# that input string against the patterns between if
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# and endif. The if..endif can nest.
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#
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# Note: do not prepend whitespace to patterns inside
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# if..endif.
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#
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# if !/pattern/flags
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#
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# endif If the input string does not match /pattern/, then
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# match that input string against the patterns
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# between if and endif. The if..endif can nest.
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#
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# blank lines and comments
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# Empty lines and whitespace-only lines are ignored,
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# as are lines whose first non-whitespace character
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# is a `#'.
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#
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# multi-line text
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# A pattern/action line starts with non-whitespace
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# text. A line that starts with whitespace continues
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# a logical line.
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#
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# TABLE SEARCH ORDER
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# For each line of message input, the patterns are applied
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# in the order as specified in the table. When a pattern is
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# found that matches the input line, the corresponding
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# action is executed and then the next input line is
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# inspected.
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#
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# TEXT SUBSTITUTION
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# Substitution of substrings from the matched expression
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# into the action string is possible using the conventional
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# Perl syntax ($1, $2, etc.). The macros in the result
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# string may need to be written as ${n} or $(n) if they
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# aren't followed by whitespace.
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#
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# Note: since negated patterns (those preceded by !) return
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# a result when the expression does not match, substitutions
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# are not available for negated patterns.
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#
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# ACTIONS
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# Action names are case insensitive. They are shown in upper
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# case for consistency with other Postfix documentation.
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#
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# BCC user@domain
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# Add the specified address as a BCC recipient, and
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# inspect the next input line. The address must have
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# a local part and domain part. The number of BCC
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# addresses that can be added is limited only by the
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# amount of available storage space.
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#
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# Note 1: the BCC address is added as if it was spec-
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# ified with NOTIFY=NONE. The sender will not be
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# notified when the BCC address is undeliverable, as
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# long as all down-stream software implements RFC
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# 3461.
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#
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# Note 2: this ignores duplicate addresses (with the
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# same delivery status notification options).
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#
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# This feature is available in Postfix 3.0 and later.
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#
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# This feature is not supported with smtp header/body
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# checks.
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#
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# DISCARD optional text...
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# Claim successful delivery and silently discard the
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# message. Do not inspect the remainder of the input
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# message. Log the optional text if specified, oth-
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# erwise log a generic message.
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#
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# Note: this action disables further header or
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# body_checks inspection of the current message and
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# affects all recipients. To discard only one recip-
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# ient without discarding the entire message, use the
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# transport(5) table to direct mail to the discard(8)
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# service.
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#
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# This feature is available in Postfix 2.0 and later.
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#
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# This feature is not supported with smtp header/body
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# checks.
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#
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# DUNNO Pretend that the input line did not match any pat-
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# tern, and inspect the next input line. This action
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# can be used to shorten the table search.
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#
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# For backwards compatibility reasons, Postfix also
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# accepts OK but it is (and always has been) treated
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# as DUNNO.
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#
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# This feature is available in Postfix 2.1 and later.
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#
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# FILTER transport:destination
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# Override the content_filter parameter setting, and
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# inspect the next input line. After the message is
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# queued, send the entire message through the speci-
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# fied external content filter. The transport name
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# specifies the first field of a mail delivery agent
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# definition in master.cf; the syntax of the next-hop
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# destination is described in the manual page of the
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# corresponding delivery agent. More information
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# about external content filters is in the Postfix
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# FILTER_README file.
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#
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# Note 1: do not use $number regular expression sub-
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# stitutions for transport or destination unless you
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# know that the information has a trusted origin.
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#
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# Note 2: this action overrides the main.cf con-
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# tent_filter setting, and affects all recipients of
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# the message. In the case that multiple FILTER
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# actions fire, only the last one is executed.
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#
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# Note 3: the purpose of the FILTER command is to
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# override message routing. To override the recipi-
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# ent's transport but not the next-hop destination,
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# specify an empty filter destination (Postfix 2.7
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# and later), or specify a transport:destination that
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# delivers through a different Postfix instance
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# (Postfix 2.6 and earlier). Other options are using
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# the recipient-dependent transport_maps or the sen-
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# der-dependent sender_dependent_default_transport-
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# _maps features.
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#
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# This feature is available in Postfix 2.0 and later.
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#
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# This feature is not supported with smtp header/body
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# checks.
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#
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# HOLD optional text...
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# Arrange for the message to be placed on the hold
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# queue, and inspect the next input line. The mes-
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# sage remains on hold until someone either deletes
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# it or releases it for delivery. Log the optional
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# text if specified, otherwise log a generic message.
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#
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# Mail that is placed on hold can be examined with
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# the postcat(1) command, and can be destroyed or
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# released with the postsuper(1) command.
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#
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# Note: use "postsuper -r" to release mail that was
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# kept on hold for a significant fraction of $maxi-
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# mal_queue_lifetime or $bounce_queue_lifetime, or
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# longer. Use "postsuper -H" only for mail that will
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# not expire within a few delivery attempts.
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#
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# Note: this action affects all recipients of the
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# message.
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#
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# This feature is available in Postfix 2.0 and later.
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#
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# This feature is not supported with smtp header/body
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# checks.
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#
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# IGNORE Delete the current line from the input, and inspect
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# the next input line. See STRIP for an alternative
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# that logs the action.
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#
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# INFO optional text...
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# Log an "info:" record with the optional text... (or
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# log a generic text), and inspect the next input
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# line. This action is useful for routine logging or
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# for debugging.
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#
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# This feature is available in Postfix 2.8 and later.
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#
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# PASS optional text...
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# Log a "pass:" record with the optional text... (or
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# log a generic text), and turn off header, body, and
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# Milter inspection for the remainder of this mes-
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# sage.
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#
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# Note: this feature relies on trust in information
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# that is easy to forge.
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#
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# This feature is available in Postfix 3.2 and later.
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#
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# This feature is not supported with smtp header/body
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# checks.
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#
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# PREPEND text...
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# Prepend one line with the specified text, and
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# inspect the next input line.
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#
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# Notes:
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#
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# o The prepended text is output on a separate
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# line, immediately before the input that
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# triggered the PREPEND action.
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#
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# o The prepended text is not considered part of
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# the input stream: it is not subject to
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# header/body checks or address rewriting, and
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# it does not affect the way that Postfix adds
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# missing message headers.
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#
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# o When prepending text before a message header
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# line, the prepended text must begin with a
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# valid message header label.
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#
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# o This action cannot be used to prepend
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# multi-line text.
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#
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# This feature is available in Postfix 2.1 and later.
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#
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# This feature is not supported with mil-
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# ter_header_checks.
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#
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# REDIRECT user@domain
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# Write a message redirection request to the queue
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# file, and inspect the next input line. After the
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# message is queued, it will be sent to the specified
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# address instead of the intended recipient(s).
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#
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# Note: this action overrides the FILTER action, and
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# affects all recipients of the message. If multiple
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# REDIRECT actions fire, only the last one is exe-
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# cuted.
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#
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# This feature is available in Postfix 2.1 and later.
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#
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# This feature is not supported with smtp header/body
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# checks.
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#
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# REPLACE text...
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# Replace the current line with the specified text,
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# and inspect the next input line.
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#
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# This feature is available in Postfix 2.2 and later.
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# The description below applies to Postfix 2.2.2 and
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# later.
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#
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# Notes:
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#
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# o When replacing a message header line, the
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# replacement text must begin with a valid
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# header label.
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#
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# o The replaced text remains part of the input
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# stream. Unlike the result from the PREPEND
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# action, a replaced message header may be
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# subject to address rewriting and may affect
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# the way that Postfix adds missing message
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# headers.
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#
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# REJECT optional text...
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# Reject the entire message. Do not inspect the
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# remainder of the input message. Reply with
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# optional text... when the optional text is speci-
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# fied, otherwise reply with a generic error message.
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#
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# Note: this action disables further header or
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# body_checks inspection of the current message and
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# affects all recipients.
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#
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# Postfix version 2.3 and later support enhanced sta-
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# tus codes. When no code is specified at the begin-
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# ning of optional text..., Postfix inserts a default
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# enhanced status code of "5.7.1".
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#
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# This feature is not supported with smtp header/body
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# checks.
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#
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# STRIP optional text...
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# Log a "strip:" record with the optional text... (or
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# log a generic text), delete the input line from the
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# input, and inspect the next input line. See IGNORE
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# for a silent alternative.
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#
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# This feature is available in Postfix 3.2 and later.
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#
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# WARN optional text...
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# Log a "warning:" record with the optional text...
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# (or log a generic text), and inspect the next input
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# line. This action is useful for debugging and for
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# testing a pattern before applying more drastic
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# actions.
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#
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# BUGS
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# Empty lines never match, because some map types mis-behave
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# when given a zero-length search string. This limitation
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# may be removed for regular expression tables in a future
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# release.
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#
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# Many people overlook the main limitations of header and
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# body_checks rules.
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#
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# o These rules operate on one logical message header
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# or one body line at a time. A decision made for one
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# line is not carried over to the next line.
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#
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# o If text in the message body is encoded (RFC 2045)
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# then the rules need to be specified for the encoded
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# form.
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#
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# o Likewise, when message headers are encoded (RFC
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# 2047) then the rules need to be specified for the
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# encoded form.
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#
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# Message headers added by the cleanup(8) daemon itself are
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# excluded from inspection. Examples of such message headers
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# are From:, To:, Message-ID:, Date:.
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#
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# Message headers deleted by the cleanup(8) daemon will be
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# examined before they are deleted. Examples are: Bcc:, Con-
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# tent-Length:, Return-Path:.
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#
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# CONFIGURATION PARAMETERS
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# body_checks
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# Lookup tables with content filter rules for message
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# body lines. These filters see one physical line at
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# a time, in chunks of at most $line_length_limit
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# bytes.
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#
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# body_checks_size_limit
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# The amount of content per message body segment
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# (attachment) that is subjected to $body_checks fil-
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# tering.
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#
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# header_checks
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#
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# mime_header_checks (default: $header_checks)
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#
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# nested_header_checks (default: $header_checks)
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# Lookup tables with content filter rules for message
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# header lines: respectively, these are applied to
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# the initial message headers (not including MIME
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# headers), to the MIME headers anywhere in the mes-
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# sage, and to the initial headers of attached mes-
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# sages.
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#
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# Note: these filters see one logical message header
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# at a time, even when a message header spans multi-
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# ple lines. Message headers that are longer than
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# $header_size_limit characters are truncated.
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#
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# disable_mime_input_processing
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# While receiving mail, give no special treatment to
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# MIME related message headers; all text after the
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# initial message headers is considered to be part of
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# the message body. This means that header_checks is
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# applied to all the initial message headers, and
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# that body_checks is applied to the remainder of the
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# message.
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#
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# Note: when used in this manner, body_checks will
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# process a multi-line message header one line at a
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# time.
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#
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# EXAMPLES
|
|
# Header pattern to block attachments with bad file name
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# extensions. For convenience, the PCRE /x flag is speci-
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# fied, so that there is no need to collapse the pattern
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# into a single line of text. The purpose of the
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# [[:xdigit:]] sub-expressions is to recognize Windows CLSID
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# strings.
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#
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# /etc/postfix/main.cf:
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# header_checks = pcre:/etc/postfix/header_checks.pcre
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#
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# /etc/postfix/header_checks.pcre:
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# /^Content-(Disposition|Type).*name\s*=\s*"?([^;]*(\.|=2E)(
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# ade|adp|asp|bas|bat|chm|cmd|com|cpl|crt|dll|exe|
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# hlp|ht[at]|
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# inf|ins|isp|jse?|lnk|md[betw]|ms[cipt]|nws|
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# \{[[:xdigit:]]{8}(?:-[[:xdigit:]]{4}){3}-[[:xdigit:]]{12}\}|
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# ops|pcd|pif|prf|reg|sc[frt]|sh[bsm]|swf|
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# vb[esx]?|vxd|ws[cfh]))(\?=)?"?\s*(;|$)/x
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# REJECT Attachment name "$2" may not end with ".$4"
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#
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# Body pattern to stop a specific HTML browser vulnerability
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# exploit.
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#
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# /etc/postfix/main.cf:
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# body_checks = regexp:/etc/postfix/body_checks
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#
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# /etc/postfix/body_checks:
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# /^<iframe src=(3D)?cid:.* height=(3D)?0 width=(3D)?0>$/
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# REJECT IFRAME vulnerability exploit
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#
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# SEE ALSO
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# cleanup(8), canonicalize and enqueue Postfix message
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# pcre_table(5), format of PCRE lookup tables
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# regexp_table(5), format of POSIX regular expression tables
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# postconf(1), Postfix configuration utility
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# postmap(1), Postfix lookup table management
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# postsuper(1), Postfix janitor
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# postcat(1), show Postfix queue file contents
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# RFC 2045, base64 and quoted-printable encoding rules
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# RFC 2047, message header encoding for non-ASCII text
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#
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# README FILES
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# Use "postconf readme_directory" or "postconf html_direc-
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# tory" to locate this information.
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# DATABASE_README, Postfix lookup table overview
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# CONTENT_INSPECTION_README, Postfix content inspection overview
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# BUILTIN_FILTER_README, Postfix built-in content inspection
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# BACKSCATTER_README, blocking returned forged mail
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#
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# LICENSE
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# The Secure Mailer license must be distributed with this
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# software.
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#
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# AUTHOR(S)
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# Wietse Venema
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# IBM T.J. Watson Research
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# P.O. Box 704
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# Yorktown Heights, NY 10598, USA
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#
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# Wietse Venema
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# Google, Inc.
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# 111 8th Avenue
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# New York, NY 10011, USA
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#
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# HEADER_CHECKS(5)
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