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# HEADER_CHECKS(5) HEADER_CHECKS(5)
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# header_checks - Postfix built-in header/body inspection
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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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# postmap -fq "string" pcre:/etc/postfix/filename
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# postmap -fq - pcre:/etc/postfix/filename <inputfile
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# Postfix provides a simple built-in content inspection
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# mechanism that examines incoming mail one message header
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# or one message body line at a time. Each input is compared
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# against a list of patterns, and when a match is found the
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# corresponding action is executed. This feature is imple-
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# mented by the Postfix cleanup(8) server.
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# For examples, see the EXAMPLES section at the end of this
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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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# Postfix supports four built-in content inspection classes:
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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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# mime_header_checks (default: $header_checks)
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# These are applied to MIME related message headers
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# This feature is available in Postfix 2.0 and later.
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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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# This feature is available in Postfix 2.0 and later.
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# These are applied to all other content, including
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# multi-part message boundaries.
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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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# 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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# 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, but
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# the slower regexp (POSIX regular expressions) support is
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# more widely available. Use the command postconf -m to
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# find out what lookup table types your Postfix system sup-
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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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# /pattern/flags action
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# When pattern matches the input string, execute the
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# corresponding action. See below for a list of pos-
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# !/pattern/flags action
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# When pattern does not match the input string, exe-
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# cute the corresponding action.
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# endif Match the input string against the patterns between
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# if and endif, if and only if the input string also
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# matches pattern. The if..endif can nest.
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# Note: do not prepend whitespace to patterns inside
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# endif Match the input string against the patterns between
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# if and endif, if and only if the input string does
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# not match pattern. The if..endif can nest.
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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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# A pattern/action line starts with non-whitespace
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# text. A line that starts with whitespace continues
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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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# 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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# 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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# 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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# DISCARD optional text...
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# Claim successful delivery and silently discard the
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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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# 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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# This feature is available in Postfix 2.0 and later.
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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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# For backwards compatibility reasons, Postfix also
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# accepts OK but it is (and always has been) treated
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# This feature is available in Postfix 2.1 and later.
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# FILTER transport:destination
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# Write a content filter request to the queue file
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# and inspect the next input line. After the com-
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# plete message is received it will be sent through
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# the specified external content filter. More infor-
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# mation about external content filters is in the
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# Postfix FILTER_README file.
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# Note: 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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# This feature is available in Postfix 2.0 and later.
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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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# 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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# Note: this action affects all recipients of the
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# This feature is available in Postfix 2.0 and later.
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# IGNORE Delete the current line from the input and inspect
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# the next input line.
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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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# Note: the prepended text is output immediately
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# before the input that triggered the PREPEND action.
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# A body action cannot prepend a message header.
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# Note: this action cannot be used to prepend multi-
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# This feature is available in Postfix 2.1 and later.
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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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# 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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# This feature is available in Postfix 2.1 and later.
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# REJECT optional text...
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# Reject the entire message. Reply with optional
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# text... when the optional text is specified, other-
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# wise reply with a generic error message.
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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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# WARN optional text...
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# Log a warning with the optional text... (or log a
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# generic message) and inspect the next input line.
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# This action is useful for debugging and for testing
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# a pattern before applying more drastic actions.
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# Many people overlook the main limitations of header and
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# body_checks rules. These rules operate on one logical
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# message header or one body line at a time, and a decision
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# made for one line is not carried over to the next line.
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# If text in the message body is encoded (RFC 2045) then the
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# rules have to specified for the encoded form. Likewise,
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# when message headers are encoded (RFC 2047) then the rules
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# need to be specified for the encoded form.
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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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# 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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# CONFIGURATION PARAMETERS
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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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# 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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# mime_header_checks (default: $header_checks)
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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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# 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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# 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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# 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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# Header pattern to block attachments with bad file name
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# /etc/postfix/main.cf:
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# header_checks = regexp:/etc/postfix/header_checks
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# /etc/postfix/header_checks:
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# /^content-(type|disposition):.*name[[:space:]]*=.*\.(exe|vbs)/
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# REJECT Bad attachment file name extension: $2
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# Body pattern to stop a specific HTML browser vulnerability
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# /etc/postfix/main.cf:
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# body_checks = regexp:/etc/postfix/body_checks
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# /etc/postfix/body_checks:
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# /^<iframe src=(3D)?cid:.* height=(3D)?0 width=(3D)?0>$/
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# REJECT IFRAME vulnerability exploit
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# 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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# 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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# The Secure Mailer license must be distributed with this
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# IBM T.J. Watson Research
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# Yorktown Heights, NY 10598, USA
added
removed
conf/header_checks
