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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-06 01:46:30 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-06 01:46:30 +0000
commitb5896ba9f6047e7031e2bdee0622d543e11a6734 (patch)
treefd7b460593a2fee1be579bec5697e6d887ea3421 /html/header_checks.5.html
parentInitial commit. (diff)
downloadpostfix-b5896ba9f6047e7031e2bdee0622d543e11a6734.tar.xz
postfix-b5896ba9f6047e7031e2bdee0622d543e11a6734.zip
Adding upstream version 3.4.23.upstream/3.4.23upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN"
+ "http://www.w3.org/TR/html4/loose.dtd">
+<html> <head>
+<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
+<title> Postfix manual - header_checks(5) </title>
+</head> <body> <pre>
+HEADER_CHECKS(5) HEADER_CHECKS(5)
+
+<b>NAME</b>
+ <a href="postconf.5.html#header_checks">header_checks</a> - Postfix built-in content inspection
+
+<b>SYNOPSIS</b>
+ <b><a href="postconf.5.html#header_checks">header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/header_checks</b>
+ <b><a href="postconf.5.html#mime_header_checks">mime_header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/mime_header_checks</b>
+ <b><a href="postconf.5.html#nested_header_checks">nested_header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/nested_header_checks</b>
+ <b><a href="postconf.5.html#body_checks">body_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/body_checks</b>
+
+ <b><a href="postconf.5.html#milter_header_checks">milter_header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/<a href="postconf.5.html#milter_header_checks">milter_header_checks</a></b>
+
+ <b><a href="postconf.5.html#smtp_header_checks">smtp_header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/smtp_header_checks</b>
+ <b><a href="postconf.5.html#smtp_mime_header_checks">smtp_mime_header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/smtp_mime_header_checks</b>
+ <b><a href="postconf.5.html#smtp_nested_header_checks">smtp_nested_header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/smtp_nested_header_checks</b>
+ <b><a href="postconf.5.html#smtp_body_checks">smtp_body_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/smtp_body_checks</b>
+
+ <b>postmap -q "</b><i>string</i><b>" <a href="pcre_table.5.html">pcre</a>:/etc/postfix/</b><i>filename</i>
+ <b>postmap -q - <a href="pcre_table.5.html">pcre</a>:/etc/postfix/</b><i>filename</i> &lt;<i>inputfile</i>
+
+<b>DESCRIPTION</b>
+ This document describes access control on the content of message head-
+ ers and message body lines; it is implemented by the Postfix <a href="cleanup.8.html"><b>cleanup</b>(8)</a>
+ server before mail is queued. See <a href="access.5.html"><b>access</b>(5)</a> 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 <a href="postconf.5.html#body_checks">body_checks</a> 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.
+
+<b>FILTERS WHILE RECEIVING MAIL</b>
+ Postfix implements the following four built-in content inspection
+ classes while receiving mail:
+
+ <b><a href="postconf.5.html#header_checks">header_checks</a></b> (default: empty)
+ These are applied to initial message headers (except for the
+ headers that are processed with <b><a href="postconf.5.html#mime_header_checks">mime_header_checks</a></b>).
+
+ <b><a href="postconf.5.html#mime_header_checks">mime_header_checks</a></b> (default: <b>$<a href="postconf.5.html#header_checks">header_checks</a></b>)
+ These are applied to MIME related message headers only.
+
+ This feature is available in Postfix 2.0 and later.
+
+ <b><a href="postconf.5.html#nested_header_checks">nested_header_checks</a></b> (default: <b>$<a href="postconf.5.html#header_checks">header_checks</a></b>)
+ These are applied to message headers of attached email messages
+ (except for the headers that are processed with
+ <b><a href="postconf.5.html#mime_header_checks">mime_header_checks</a></b>).
+
+ This feature is available in Postfix 2.0 and later.
+
+ <b><a href="postconf.5.html#body_checks">body_checks</a></b>
+ 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.
+
+<b>FILTERS AFTER RECEIVING MAIL</b>
+ Postfix supports a subset of the built-in content inspection classes
+ after the message is received:
+
+ <b><a href="postconf.5.html#milter_header_checks">milter_header_checks</a></b> (default: empty)
+ These are applied to headers that are added with Milter applica-
+ tions.
+
+ This feature is available in Postfix 2.7 and later.
+
+<b>FILTERS WHILE DELIVERING MAIL</b>
+ Postfix supports all four content inspection classes while delivering
+ mail via SMTP.
+
+ <b><a href="postconf.5.html#smtp_header_checks">smtp_header_checks</a></b> (default: empty)
+
+ <b><a href="postconf.5.html#smtp_mime_header_checks">smtp_mime_header_checks</a></b> (default: empty)
+
+ <b><a href="postconf.5.html#smtp_nested_header_checks">smtp_nested_header_checks</a></b> (default: empty)
+
+ <b><a href="postconf.5.html#smtp_body_checks">smtp_body_checks</a></b> (default: empty)
+ These features are available in Postfix 2.5 and later.
+
+<b>COMPATIBILITY</b>
+ With Postfix version 2.2 and earlier specify "<b>postmap -fq</b>" to query a
+ table that contains case sensitive patterns. By default, <a href="regexp_table.5.html">regexp</a>: and
+ <a href="pcre_table.5.html">pcre</a>: patterns are case insensitive.
+
+<b>TABLE FORMAT</b>
+ This document assumes that header and <a href="postconf.5.html#body_checks">body_checks</a> rules are specified
+ in the form of Postfix regular expression lookup tables. Usually the
+ best performance is obtained with <b>pcre</b> (Perl Compatible Regular Expres-
+ sion) tables. The <b>regexp</b> (POSIX regular expressions) tables are usually
+ slower, but more widely available. Use the command "<b>postconf -m</b>" 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 <a href="pcre_table.5.html"><b>pcre_table</b>(5)</a>
+ or <a href="regexp_table.5.html"><b>regexp_table</b>(5)</a>, respectively.
+
+ <b>/</b><i>pattern</i><b>/</b><i>flags action</i>
+ When /<i>pattern</i>/ matches the input string, execute the correspond-
+ ing <i>action</i>. See below for a list of possible actions.
+
+ <b>!/</b><i>pattern</i><b>/</b><i>flags action</i>
+ When /<i>pattern</i>/ does <b>not</b> match the input string, execute the cor-
+ responding <i>action</i>.
+
+ <b>if /</b><i>pattern</i><b>/</b><i>flags</i>
+
+ <b>endif</b> If the input string matches /<i>pattern</i>/, then match that input
+ string against the patterns between <b>if</b> and <b>endif</b>. The <b>if</b>..<b>endif</b>
+ can nest.
+
+ Note: do not prepend whitespace to patterns inside <b>if</b>..<b>endif</b>.
+
+ <b>if !/</b><i>pattern</i><b>/</b><i>flags</i>
+
+ <b>endif</b> If the input string does not match /<i>pattern</i>/, then match that
+ input string against the patterns between <b>if</b> and <b>endif</b>. The
+ <b>if</b>..<b>endif</b> 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.
+
+<b>TABLE SEARCH ORDER</b>
+ 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.
+
+<b>TEXT SUBSTITUTION</b>
+ Substitution of substrings from the matched expression into the <i>action</i>
+ string is possible using the conventional Perl syntax (<b>$1</b>, <b>$2</b>, etc.).
+ The macros in the result string may need to be written as <b>${n}</b> or <b>$(n)</b>
+ if they aren't followed by whitespace.
+
+ Note: since negated patterns (those preceded by <b>!</b>) return a result when
+ the expression does not match, substitutions are not available for
+ negated patterns.
+
+<b>ACTIONS</b>
+ Action names are case insensitive. They are shown in upper case for
+ consistency with other Postfix documentation.
+
+ <b>BCC</b> <i>user@domain</i>
+ 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 <a href="http://tools.ietf.org/html/rfc3461">RFC 3461</a>.
+
+ 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.
+
+ <b>DISCARD</b> <i>optional text...</i>
+ 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 <a href="postconf.5.html#body_checks">body_checks</a> inspec-
+ tion of the current message and affects all recipients. To dis-
+ card only one recipient without discarding the entire message,
+ use the <a href="transport.5.html">transport(5)</a> table to direct mail to the <a href="discard.8.html">discard(8)</a> ser-
+ vice.
+
+ This feature is available in Postfix 2.0 and later.
+
+ This feature is not supported with smtp header/body checks.
+
+ <b>DUNNO</b> 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 <b>OK</b> but
+ it is (and always has been) treated as <b>DUNNO</b>.
+
+ This feature is available in Postfix 2.1 and later.
+
+ <b>FILTER</b> <i>transport:destination</i>
+ Override the <a href="postconf.5.html#content_filter">content_filter</a> parameter setting, and inspect the
+ next input line. After the message is queued, send the entire
+ message through the specified external content filter. The
+ <i>transport</i> name specifies the first field of a mail delivery
+ agent definition in <a href="master.5.html">master.cf</a>; the syntax of the next-hop <i>desti-</i>
+ <i>nation</i> is described in the manual page of the corresponding
+ delivery agent. More information about external content filters
+ is in the Postfix <a href="FILTER_README.html">FILTER_README</a> file.
+
+ Note 1: do not use $<i>number</i> regular expression substitutions for
+ <i>transport</i> or <i>destination</i> unless you know that the information
+ has a trusted origin.
+
+ Note 2: this action overrides the <a href="postconf.5.html">main.cf</a> <b><a href="postconf.5.html#content_filter">content_filter</a></b> set-
+ ting, and affects all recipients of the message. In the case
+ that multiple <b>FILTER</b> actions fire, only the last one is exe-
+ cuted.
+
+ Note 3: the purpose of the FILTER command is to override message
+ routing. To override the recipient's <i>transport</i> but not the
+ next-hop <i>destination</i>, specify an empty filter <i>destination</i> (Post-
+ fix 2.7 and later), or specify a <i>transport:destination</i> that
+ delivers through a different Postfix instance (Postfix 2.6 and
+ earlier). Other options are using the recipient-dependent <b><a href="postconf.5.html#transport_maps">trans</a>-</b>
+ <b><a href="postconf.5.html#transport_maps">port_maps</a></b> or the sender-dependent <b><a href="postconf.5.html#sender_dependent_default_transport_maps">sender_dependent_default-</b>
+ <b>_transport_maps</a></b> features.
+
+ This feature is available in Postfix 2.0 and later.
+
+ This feature is not supported with smtp header/body checks.
+
+ <b>HOLD</b> <i>optional text...</i>
+ Arrange for the message to be placed on the <b>hold</b> queue, and
+ inspect the next input line. The message remains on <b>hold</b> until
+ someone either deletes it or releases it for delivery. Log the
+ optional text if specified, otherwise log a generic message.
+
+ Mail that is placed on hold can be examined with the <a href="postcat.1.html"><b>postcat</b>(1)</a>
+ command, and can be destroyed or released with the <a href="postsuper.1.html"><b>postsuper</b>(1)</a>
+ command.
+
+ Note: use "<b>postsuper -r</b>" to release mail that was kept on hold
+ for a significant fraction of <b>$<a href="postconf.5.html#maximal_queue_lifetime">maximal_queue_lifetime</a></b> or
+ <b>$<a href="postconf.5.html#bounce_queue_lifetime">bounce_queue_lifetime</a></b>, or longer. Use "<b>postsuper -H</b>" 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.
+
+ <b>IGNORE</b> Delete the current line from the input, and inspect the next
+ input line. See <b>STRIP</b> for an alternative that logs the action.
+
+ <b>INFO</b> <i>optional text...</i>
+ Log an "info:" record with the <i>optional text...</i> (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.
+
+ <b>PASS</b> <i>optional text...</i>
+ Log a "pass:" record with the <i>optional text...</i> (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.
+
+ <b>PREPEND</b> <i>text...</i>
+ Prepend one line with the specified text, and inspect the next
+ input line.
+
+ Notes:
+
+ <b>o</b> The prepended text is output on a separate line, immedi-
+ ately before the input that triggered the <b>PREPEND</b> action.
+
+ <b>o</b> 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.
+
+ <b>o</b> When prepending text before a message header line, the
+ prepended text must begin with a valid message header
+ label.
+
+ <b>o</b> 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 <a href="postconf.5.html#milter_header_checks">milter_header_checks</a>.
+
+ <b>REDIRECT</b> <i>user@domain</i>
+ 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 <b>FILTER</b> action, and affects all
+ recipients of the message. If multiple <b>REDIRECT</b> 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.
+
+ <b>REPLACE</b> <i>text...</i>
+ 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:
+
+ <b>o</b> When replacing a message header line, the replacement
+ text must begin with a valid header label.
+
+ <b>o</b> The replaced text remains part of the input stream.
+ Unlike the result from the <b>PREPEND</b> action, a replaced
+ message header may be subject to address rewriting and
+ may affect the way that Postfix adds missing message
+ headers.
+
+ <b>REJECT</b> <i>optional text...</i>
+ Reject the entire message. Do not inspect the remainder of the
+ input message. Reply with <i>optional text...</i> when the optional
+ text is specified, otherwise reply with a generic error message.
+
+ Note: this action disables further header or <a href="postconf.5.html#body_checks">body_checks</a> 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 <i>optional text...</i>,
+ Postfix inserts a default enhanced status code of "5.7.1".
+
+ This feature is not supported with smtp header/body checks.
+
+ <b>STRIP</b> <i>optional text...</i>
+ Log a "strip:" record with the <i>optional text...</i> (or log a
+ generic text), delete the input line from the input, and inspect
+ the next input line. See <b>IGNORE</b> for a silent alternative.
+
+ This feature is available in Postfix 3.2 and later.
+
+ <b>WARN</b> <i>optional text...</i>
+ Log a "warning:" record with the <i>optional text...</i> (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.
+
+<b>BUGS</b>
+ 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 <a href="postconf.5.html#body_checks">body_checks</a>
+ rules.
+
+ <b>o</b> 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.
+
+ <b>o</b> If text in the message body is encoded (<a href="http://tools.ietf.org/html/rfc2045">RFC 2045</a>) then the rules
+ need to be specified for the encoded form.
+
+ <b>o</b> Likewise, when message headers are encoded (<a href="http://tools.ietf.org/html/rfc2047">RFC 2047</a>) then the
+ rules need to be specified for the encoded form.
+
+ Message headers added by the <a href="cleanup.8.html"><b>cleanup</b>(8)</a> daemon itself are excluded from
+ inspection. Examples of such message headers are <b>From:</b>, <b>To:</b>, <b>Mes-</b>
+ <b>sage-ID:</b>, <b>Date:</b>.
+
+ Message headers deleted by the <a href="cleanup.8.html"><b>cleanup</b>(8)</a> daemon will be examined
+ before they are deleted. Examples are: <b>Bcc:</b>, <b>Content-Length:</b>,
+ <b>Return-Path:</b>.
+
+<b>CONFIGURATION PARAMETERS</b>
+ <b><a href="postconf.5.html#body_checks">body_checks</a></b>
+ Lookup tables with content filter rules for message body lines.
+ These filters see one physical line at a time, in chunks of at
+ most <b>$<a href="postconf.5.html#line_length_limit">line_length_limit</a></b> bytes.
+
+ <b><a href="postconf.5.html#body_checks_size_limit">body_checks_size_limit</a></b>
+ The amount of content per message body segment (attachment) that
+ is subjected to <b>$<a href="postconf.5.html#body_checks">body_checks</a></b> filtering.
+
+ <b><a href="postconf.5.html#header_checks">header_checks</a></b>
+
+ <b><a href="postconf.5.html#mime_header_checks">mime_header_checks</a></b> (default: <b>$<a href="postconf.5.html#header_checks">header_checks</a></b>)
+
+ <b><a href="postconf.5.html#nested_header_checks">nested_header_checks</a></b> (default: <b>$<a href="postconf.5.html#header_checks">header_checks</a></b>)
+ Lookup tables with content filter rules for message header
+ lines: respectively, these are applied to the initial message
+ headers (not including MIME headers), to the MIME headers any-
+ where in the message, and to the initial headers of attached
+ messages.
+
+ Note: these filters see one logical message header at a time,
+ even when a message header spans multiple lines. Message headers
+ that are longer than <b>$<a href="postconf.5.html#header_size_limit">header_size_limit</a></b> characters are trun-
+ cated.
+
+ <b><a href="postconf.5.html#disable_mime_input_processing">disable_mime_input_processing</a></b>
+ 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
+ <b><a href="postconf.5.html#header_checks">header_checks</a></b> is applied to all the initial message headers, and
+ that <b><a href="postconf.5.html#body_checks">body_checks</a></b> is applied to the remainder of the message.
+
+ Note: when used in this manner, <b><a href="postconf.5.html#body_checks">body_checks</a></b> will process a
+ multi-line message header one line at a time.
+
+<b>EXAMPLES</b>
+ 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/<a href="postconf.5.html">main.cf</a>:
+ <a href="postconf.5.html#header_checks">header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/header_checks.pcre
+
+ /etc/postfix/header_checks.<a href="pcre_table.5.html">pcre</a>:
+ /^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 ".$4"
+
+ Body pattern to stop a specific HTML browser vulnerability exploit.
+
+ /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ <a href="postconf.5.html#body_checks">body_checks</a> = <a href="regexp_table.5.html">regexp</a>:/etc/postfix/body_checks
+
+ /etc/postfix/body_checks:
+ /^&lt;iframe src=(3D)?cid:.* height=(3D)?0 width=(3D)?0&gt;$/
+ REJECT IFRAME vulnerability exploit
+
+<b>SEE ALSO</b>
+ <a href="cleanup.8.html">cleanup(8)</a>, canonicalize and enqueue Postfix message
+ <a href="pcre_table.5.html">pcre_table(5)</a>, format of PCRE lookup tables
+ <a href="regexp_table.5.html">regexp_table(5)</a>, format of POSIX regular expression tables
+ <a href="postconf.1.html">postconf(1)</a>, Postfix configuration utility
+ <a href="postmap.1.html">postmap(1)</a>, Postfix lookup table management
+ <a href="postsuper.1.html">postsuper(1)</a>, Postfix janitor
+ <a href="postcat.1.html">postcat(1)</a>, show Postfix queue file contents
+ <a href="http://tools.ietf.org/html/rfc2045">RFC 2045</a>, base64 and quoted-printable encoding rules
+ <a href="http://tools.ietf.org/html/rfc2047">RFC 2047</a>, message header encoding for non-ASCII text
+
+<b>README FILES</b>
+ <a href="DATABASE_README.html">DATABASE_README</a>, Postfix lookup table overview
+ <a href="CONTENT_INSPECTION_README.html">CONTENT_INSPECTION_README</a>, Postfix content inspection overview
+ <a href="BUILTIN_FILTER_README.html">BUILTIN_FILTER_README</a>, Postfix built-in content inspection
+ <a href="BACKSCATTER_README.html">BACKSCATTER_README</a>, blocking returned forged mail
+
+<b>LICENSE</b>
+ The Secure Mailer license must be distributed with this software.
+
+<b>AUTHOR(S)</b>
+ 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)
+</pre> </body> </html>