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Updated: Thursday, June 13, 2019
 
 

body_checks (5)

Name

body_checks - 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

HEADER_CHECKS(5)              File Formats Manual             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 head-
       ers 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 exam-
       ined 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 attachments, and they do not unzip
       archives.  See  the documents referenced below in the README FILES sec-
       tion 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 content.

FILTERS AFTER RECEIVING MAIL
       Postfix supports a subset of the built-in  content  inspection  classes
       after the message is received:

       milter_header_checks (default: empty)
              These are applied to headers that are added with Milter applica-
              tions.

              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 Expres-
       sion) tables. The regexp (POSIX regular expressions) tables are usually
       slower,  but  more  widely available.  Use the command "postconf -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 correspond-
              ing action. See below for a list of possible actions.

       !/pattern/flags action
              When /pattern/ does not match the input string, execute the cor-
              responding 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  specified  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, otherwise log a generic message.

              Note: this action disables further header or body_checks inspec-
              tion of the current message and affects all recipients.  To dis-
              card only one recipient without discarding the  entire  message,
              use the transport(5) table to direct mail to the discard(8) ser-
              vice.

              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  pattern,  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  specified  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 desti-
              nation 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 substitutions  for
              transport  or  destination  unless you know that the information
              has a trusted origin.

              Note 2: this action overrides the  main.cf  content_filter  set-
              ting,  and  affects  all  recipients of the message. In the case
              that multiple FILTER actions fire, only the  last  one  is  exe-
              cuted.

              Note 3: the purpose of the FILTER command is to override message
              routing.  To override the  recipient's  transport  but  not  the
              next-hop destination, specify an empty filter destination (Post-
              fix 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 trans-
              port_maps   or  the  sender-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 message 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   $maximal_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 message.

              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, immedi-
                     ately 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 milter_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 executed.

              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 descrip-
              tion 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 specified, otherwise reply with a generic error message.

              Note: this action disables further header or body_checks inspec-
              tion of the current message and affects all recipients.

              Postfix version 2.3 and later  support  enhanced  status  codes.
              When  no code is specified at the beginning 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:, Mes-
       sage-ID:, Date:.

       Message headers deleted by  the  cleanup(8)  daemon  will  be  examined
       before   they   are   deleted.  Examples  are:  Bcc:,  Content-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 filtering.

       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 any-
              where in the message, and to the  initial  headers  of  attached
              messages.

              Note:  these  filters  see one logical message header at a time,
              even when a message header spans multiple lines. Message headers
              that  are  longer  than  $header_size_limit characters are trun-
              cated.

       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 specified, 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


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------------------+
       |ATTRIBUTE TYPE |       ATTRIBUTE VALUE        |
       +---------------+------------------------------+
       |Availability   | service/network/smtp/postfix |
       +---------------+------------------------------+
       |Stability      | Volatile                     |
       +---------------+------------------------------+
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_directory" 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



NOTES
       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from  https://archive.mgm51.com/mirrors/postfix-
       source/official/postfix-3.2.2.tar.gz

       Further information about this software can be found on the open source
       community website at http://www.postfix.org.



                                                              HEADER_CHECKS(5)