Postfix header_checks configuration example for CentOS Linux 8

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)

    
  

Config Details

Location
/etc/postfix/header_checks
Operating system
CentOS Linux 8
Length
549 lines
MD5 checksum
646be960e1fbfe0a341f52dbbb8c1988

Usage

Download the raw file with wget or curl

Wget

wget -O header_checks.example https://exampleconfig.com/static/raw/postfix/centos8/etc/postfix/header_checks

cURL

curl https://exampleconfig.com/static/raw/postfix/centos8/etc/postfix/header_checks > header_checks.example