Get the default configuration file header_checks for Postfix, optimized for CentOS Linux 8. This example configuration ensures optimal compatibility and performance for Postfix, making it easy to set up and adjust to meet your needs.
Find and download the configuration file here: /etc/postfix/header_checks.
For more configurations and setup guides, visit our related files section to further customize your system.
# HEADER_CHECKS(5) HEADER_CHECKS(5)
#
# NAME
# header_checks - Postfix built-in content inspection
#
# SYNOPSIS
# header_checks = pcre:/etc/postfix/header_checks
# mime_header_checks = pcre:/etc/postfix/mime_header_checks
# nested_header_checks = pcre:/etc/postfix/nested_header_checks
# body_checks = pcre:/etc/postfix/body_checks
#
# milter_header_checks = pcre:/etc/postfix/milter_header_checks
#
# smtp_header_checks = pcre:/etc/postfix/smtp_header_checks
# smtp_mime_header_checks = pcre:/etc/postfix/smtp_mime_header_checks
# smtp_nested_header_checks = pcre:/etc/postfix/smtp_nested_header_checks
# smtp_body_checks = pcre:/etc/postfix/smtp_body_checks
#
# postmap -q "string" pcre:/etc/postfix/filename
# postmap -q - pcre:/etc/postfix/filename <inputfile
#
# DESCRIPTION
# This document describes access control on the content of
# message headers and message body lines; it is implemented
# by the Postfix cleanup(8) server before mail is queued.
# See access(5) for access control on remote SMTP client
# information.
#
# Each message header or message body line is compared
# against a list of patterns. When a match is found the
# corresponding action is executed, and the matching process
# is repeated for the next message header or message body
# line.
#
# Note: message headers are examined one logical header at a
# time, even when a message header spans multiple lines.
# Body lines are always examined one line at a time.
#
# For examples, see the EXAMPLES section at the end of this
# manual page.
#
# Postfix header or body_checks are designed to stop a flood
# of mail from worms or viruses; they do not decode attach-
# ments, and they do not unzip archives. See the documents
# referenced below in the README FILES section if you need
# more sophisticated content analysis.
#
# FILTERS WHILE RECEIVING MAIL
# Postfix implements the following four built-in content
# inspection classes while receiving mail:
#
# header_checks (default: empty)
# These are applied to initial message headers
# (except for the headers that are processed with
# mime_header_checks).
#
# mime_header_checks (default: $header_checks)
# These are applied to MIME related message headers
# only.
#
# This feature is available in Postfix 2.0 and later.
#
# nested_header_checks (default: $header_checks)
# These are applied to message headers of attached
# email messages (except for the headers that are
# processed with mime_header_checks).
#
# This feature is available in Postfix 2.0 and later.
#
# body_checks
# These are applied to all other content, including
# multi-part message boundaries.
#
# With Postfix versions before 2.0, all content after
# the initial message headers is treated as body con-
# tent.
#
# FILTERS AFTER RECEIVING MAIL
# Postfix supports a subset of the built-in content inspec-
# tion classes after the message is received:
#
# milter_header_checks (default: empty)
# These are applied to headers that are added with
# Milter applications.
#
# This feature is available in Postfix 2.7 and later.
#
# FILTERS WHILE DELIVERING MAIL
# Postfix supports all four content inspection classes while
# delivering mail via SMTP.
#
# smtp_header_checks (default: empty)
#
# smtp_mime_header_checks (default: empty)
#
# smtp_nested_header_checks (default: empty)
#
# smtp_body_checks (default: empty)
# These features are available in Postfix 2.5 and
# later.
#
# COMPATIBILITY
# With Postfix version 2.2 and earlier specify "postmap -fq"
# to query a table that contains case sensitive patterns. By
# default, regexp: and pcre: patterns are case insensitive.
#
# TABLE FORMAT
# This document assumes that header and body_checks rules
# are specified in the form of Postfix regular expression
# lookup tables. Usually the best performance is obtained
# with pcre (Perl Compatible Regular Expression) tables. The
# regexp (POSIX regular expressions) tables are usually
# slower, but more widely available. Use the command "post-
# conf -m" to find out what lookup table types your Postfix
# system supports.
#
# The general format of Postfix regular expression tables is
# given below. For a discussion of specific pattern or
# flags syntax, see pcre_table(5) or regexp_table(5),
# respectively.
#
# /pattern/flags action
# When /pattern/ matches the input string, execute
# the corresponding action. See below for a list of
# possible actions.
#
# !/pattern/flags action
# When /pattern/ does not match the input string,
# execute the corresponding action.
#
# 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.
#
# 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.
#
# 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 pattern/action line starts with non-whitespace
# text. A line that starts with whitespace continues
# a logical line.
#
# TABLE SEARCH ORDER
# For each line of message input, the patterns are applied
# in the order as specified in the table. When a pattern is
# found that matches the input line, the corresponding
# action is executed and then the next input line is
# inspected.
#
# TEXT SUBSTITUTION
# Substitution of substrings from the matched expression
# into the action string is possible using the conventional
# Perl syntax ($1, $2, etc.). 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.
#
# ACTIONS
# Action names are case insensitive. They are shown in upper
# case for consistency with other Postfix documentation.
#
# BCC user@domain
# Add the specified address as a BCC recipient, and
# inspect the next input line. The address must have
# a local part and domain part. The number of BCC
# addresses that can be added is limited only by the
# amount of available storage space.
#
# Note 1: the BCC address is added as if it was spec-
# ified with NOTIFY=NONE. The sender will not be
# notified when the BCC address is undeliverable, as
# long as all down-stream software implements RFC
# 3461.
#
# Note 2: this ignores duplicate addresses (with the
# same delivery status notification options).
#
# This feature is available in Postfix 3.0 and later.
#
# This feature is not supported with smtp header/body
# checks.
#
# DISCARD optional text...
# Claim successful delivery and silently discard the
# message. Do not inspect the remainder of the input
# message. Log the optional text if specified, oth-
# erwise log a generic message.
#
# Note: this action disables further header or
# body_checks inspection of the current message and
# affects all recipients. To discard only one recip-
# ient without discarding the entire message, use the
# transport(5) table to direct mail to the discard(8)
# service.
#
# This feature is available in Postfix 2.0 and later.
#
# This feature is not supported with smtp header/body
# checks.
#
# DUNNO Pretend that the input line did not match any pat-
# tern, and inspect the next input line. This action
# can be used to shorten the table search.
#
# For backwards compatibility reasons, Postfix also
# accepts OK but it is (and always has been) treated
# as DUNNO.
#
# This feature is available in Postfix 2.1 and later.
#
# FILTER transport:destination
# Override the content_filter parameter setting, and
# inspect the next input line. After the message is
# queued, send the entire message through the speci-
# fied external content filter. The transport name
# specifies the first field of a mail delivery agent
# definition in master.cf; the syntax of the next-hop
# destination is described in the manual page of the
# corresponding delivery agent. More information
# about external content filters is in the Postfix
# FILTER_README file.
#
# Note 1: do not use $number regular expression sub-
# stitutions for transport or destination unless you
# know that the information has a trusted origin.
#
# Note 2: this action overrides the main.cf con-
# tent_filter setting, and affects all recipients of
# the message. In the case that multiple FILTER
# actions fire, only the last one is executed.
#
# Note 3: the purpose of the FILTER command is to
# override message routing. To override the recipi-
# ent's transport but not the next-hop destination,
# specify an empty filter destination (Postfix 2.7
# and later), or specify a transport:destination that
# delivers through a different Postfix instance
# (Postfix 2.6 and earlier). Other options are using
# the recipient-dependent transport_maps or the sen-
# der-dependent sender_dependent_default_transport-
# _maps features.
#
# This feature is available in Postfix 2.0 and later.
#
# This feature is not supported with smtp header/body
# checks.
#
# HOLD optional text...
# Arrange for the message to be placed on the hold
# queue, and inspect the next input line. The mes-
# sage remains on hold until someone either deletes
# it or releases it for delivery. Log the optional
# text if specified, otherwise log a generic message.
#
# Mail that is placed on hold can be examined with
# the postcat(1) command, and can be destroyed or
# released with the postsuper(1) command.
#
# Note: use "postsuper -r" to release mail that was
# kept on hold for a significant fraction of $maxi-
# mal_queue_lifetime or $bounce_queue_lifetime, or
# longer. Use "postsuper -H" only for mail that will
# not expire within a few delivery attempts.
#
# Note: this action affects all recipients of the
# message.
#
# This feature is available in Postfix 2.0 and later.
#
# This feature is not supported with smtp header/body
# checks.
#
# IGNORE Delete the current line from the input, and inspect
# the next input line. See STRIP for an alternative
# that logs the action.
#
# INFO optional text...
# Log an "info:" record with the optional text... (or
# log a generic text), and inspect the next input
# line. This action is useful for routine logging or
# for debugging.
#
# This feature is available in Postfix 2.8 and later.
#
# PASS optional text...
# Log a "pass:" record with the optional text... (or
# log a generic text), and turn off header, body, and
# Milter inspection for the remainder of this mes-
# sage.
#
# Note: this feature relies on trust in information
# that is easy to forge.
#
# This feature is available in Postfix 3.2 and later.
#
# This feature is not supported with smtp header/body
# checks.
#
# PREPEND text...
# Prepend one line with the specified text, and
# inspect the next input line.
#
# Notes:
#
# o The prepended text is output on a separate
# line, immediately before the input that
# triggered the PREPEND action.
#
# o The prepended text is not considered part of
# the input stream: it is not subject to
# header/body checks or address rewriting, and
# it does not affect the way that Postfix adds
# missing message headers.
#
# o When prepending text before a message header
# line, the prepended text must begin with a
# valid message header label.
#
# o This action cannot be used to prepend
# multi-line text.
#
# This feature is available in Postfix 2.1 and later.
#
# This feature is not supported with mil-
# ter_header_checks.
#
# REDIRECT user@domain
# Write a message redirection request to the queue
# file, and inspect the next input line. After the
# message is queued, it will be sent to the specified
# address instead of the intended recipient(s).
#
# Note: this action overrides the FILTER action, and
# affects all recipients of the message. If multiple
# REDIRECT actions fire, only the last one is exe-
# cuted.
#
# This feature is available in Postfix 2.1 and later.
#
# This feature is not supported with smtp header/body
# checks.
#
# REPLACE text...
# Replace the current line with the specified text,
# and inspect the next input line.
#
# This feature is available in Postfix 2.2 and later.
# The description below applies to Postfix 2.2.2 and
# later.
#
# Notes:
#
# o When replacing a message header line, the
# replacement text must begin with a valid
# header label.
#
# o The replaced text remains part of the input
# stream. Unlike the result from the PREPEND
# action, a replaced message header may be
# subject to address rewriting and may affect
# the way that Postfix adds missing message
# headers.
#
# REJECT optional text...
# Reject the entire message. Do not inspect the
# remainder of the input message. Reply with
# optional text... when the optional text is speci-
# fied, otherwise reply with a generic error message.
#
# Note: this action disables further header or
# body_checks inspection of the current message and
# affects all recipients.
#
# Postfix version 2.3 and later support enhanced sta-
# tus codes. When no code is specified at the begin-
# ning of optional text..., Postfix inserts a default
# enhanced status code of "5.7.1".
#
# This feature is not supported with smtp header/body
# checks.
#
# STRIP optional text...
# Log a "strip:" record with the optional text... (or
# log a generic text), delete the input line from the
# input, and inspect the next input line. See IGNORE
# for a silent alternative.
#
# This feature is available in Postfix 3.2 and later.
#
# WARN optional text...
# Log a "warning:" record with the optional text...
# (or log a generic text), and inspect the next input
# line. This action is useful for debugging and for
# testing a pattern before applying more drastic
# actions.
#
# BUGS
# Empty lines never match, because some map types mis-behave
# when given a zero-length search string. This limitation
# may be removed for regular expression tables in a future
# release.
#
# Many people overlook the main limitations of header and
# body_checks rules.
#
# o These rules operate on one logical message header
# or one body line at a time. A decision made for one
# line is not carried over to the next line.
#
# o If text in the message body is encoded (RFC 2045)
# then the rules need to be specified for the encoded
# form.
#
# o Likewise, when message headers are encoded (RFC
# 2047) then the rules need to be specified for the
# encoded form.
#
# Message headers added by the cleanup(8) daemon itself are
# excluded from inspection. Examples of such message headers
# are From:, To:, Message-ID:, Date:.
#
# Message headers deleted by the cleanup(8) daemon will be
# examined before they are deleted. Examples are: Bcc:, Con-
# tent-Length:, Return-Path:.
#
# CONFIGURATION PARAMETERS
# body_checks
# Lookup tables with content filter rules for message
# body lines. These filters see one physical line at
# a time, in chunks of at most $line_length_limit
# bytes.
#
# body_checks_size_limit
# The amount of content per message body segment
# (attachment) that is subjected to $body_checks fil-
# tering.
#
# header_checks
#
# mime_header_checks (default: $header_checks)
#
# nested_header_checks (default: $header_checks)
# Lookup tables with content filter rules for message
# header lines: respectively, these are applied to
# the initial message headers (not including MIME
# headers), to the MIME headers anywhere in the mes-
# sage, and to the initial headers of attached mes-
# sages.
#
# Note: these filters see one logical message header
# at a time, even when a message header spans multi-
# ple lines. Message headers that are longer than
# $header_size_limit characters are truncated.
#
# disable_mime_input_processing
# While receiving mail, give no special treatment to
# MIME related message headers; all text after the
# initial message headers is considered to be part of
# the message body. This means that header_checks is
# applied to all the initial message headers, and
# that body_checks is applied to the remainder of the
# message.
#
# Note: when used in this manner, body_checks will
# process a multi-line message header one line at a
# time.
#
# EXAMPLES
# Header pattern to block attachments with bad file name
# extensions. For convenience, the PCRE /x flag is speci-
# fied, so that there is no need to collapse the pattern
# into a single line of text. The purpose of the
# [[:xdigit:]] sub-expressions is to recognize Windows CLSID
# strings.
#
# /etc/postfix/main.cf:
# header_checks = pcre:/etc/postfix/header_checks.pcre
#
# /etc/postfix/header_checks.pcre:
# /^Content-(Disposition|Type).*name\s*=\s*"?([^;]*(\.|=2E)(
# ade|adp|asp|bas|bat|chm|cmd|com|cpl|crt|dll|exe|
# hlp|ht[at]|
# inf|ins|isp|jse?|lnk|md[betw]|ms[cipt]|nws|
# \{[[:xdigit:]]{8}(?:-[[:xdigit:]]{4}){3}-[[:xdigit:]]{12}\}|
# ops|pcd|pif|prf|reg|sc[frt]|sh[bsm]|swf|
# vb[esx]?|vxd|ws[cfh]))(\?=)?"?\s*(;|$)/x
# REJECT Attachment name "$2" may not end with ".$4"
#
# Body pattern to stop a specific HTML browser vulnerability
# exploit.
#
# /etc/postfix/main.cf:
# body_checks = regexp:/etc/postfix/body_checks
#
# /etc/postfix/body_checks:
# /^<iframe src=(3D)?cid:.* height=(3D)?0 width=(3D)?0>$/
# REJECT IFRAME vulnerability exploit
#
# SEE ALSO
# cleanup(8), canonicalize and enqueue Postfix message
# pcre_table(5), format of PCRE lookup tables
# regexp_table(5), format of POSIX regular expression tables
# postconf(1), Postfix configuration utility
# postmap(1), Postfix lookup table management
# postsuper(1), Postfix janitor
# postcat(1), show Postfix queue file contents
# RFC 2045, base64 and quoted-printable encoding rules
# RFC 2047, message header encoding for non-ASCII text
#
# README FILES
# Use "postconf readme_directory" or "postconf html_direc-
# tory" to locate this information.
# DATABASE_README, Postfix lookup table overview
# CONTENT_INSPECTION_README, Postfix content inspection overview
# BUILTIN_FILTER_README, Postfix built-in content inspection
# BACKSCATTER_README, blocking returned forged mail
#
# LICENSE
# The Secure Mailer license must be distributed with this
# software.
#
# AUTHOR(S)
# 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
#
# HEADER_CHECKS(5)
Download the raw file with wget or curl
wget -O header_checks.example https://exampleconfig.com/static/raw/postfix/centos8/etc/postfix/header_checks
curl https://exampleconfig.com/static/raw/postfix/centos8/etc/postfix/header_checks > header_checks.example
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