postfix-master/header_checks.5.html

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   7 HEADER_CHECKS(5)                                              HEADER_CHECKS(5)
   8
   9 <b>NAME</b>
  10        <a href="postconf.5.html#header_checks">header_checks</a> - Postfix built-in content inspection
  11
  12 <b>SYNOPSIS</b>
  13        <b><a href="postconf.5.html#header_checks">header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/header_checks</b>
  14        <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>
  15        <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>
  16        <b><a href="postconf.5.html#body_checks">body_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/body_checks</b>
  17
  18        <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>
  19
  20        <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>
  21        <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>
  22        <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>
  23        <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>
  24
  25        <b>postmap -q "</b><i>string</i><b>" <a href="pcre_table.5.html">pcre</a>:/etc/postfix/</b><i>filename</i>
  26        <b>postmap -q - <a href="pcre_table.5.html">pcre</a>:/etc/postfix/</b><i>filename</i> &lt;<i>inputfile</i>
  27
  28 <b>DESCRIPTION</b>
  29        This  document  describes access control on the content of
  30        message headers and message body lines; it is  implemented
  31        by  the  Postfix  <a href="cleanup.8.html"><b>cleanup</b>(8)</a> server before mail is queued.
  32        See <a href="access.5.html"><b>access</b>(5)</a> for access control  on  remote  SMTP  client
  33        information.
  34
  35        Each  message  header  or  message  body  line is compared
  36        against a list of patterns.  When a  match  is  found  the
  37        corresponding action is executed, and the matching process
  38        is repeated for the next message header  or  message  body
  39        line.
  40
  41        Note: message headers are examined one logical header at a
  42        time, even when a message  header  spans  multiple  lines.
  43        Body lines are always examined one line at a time.
  44
  45        For  examples, see the EXAMPLES section at the end of this
  46        manual page.
  47
  48        Postfix header or <a href="postconf.5.html#body_checks">body_checks</a> are designed to stop a flood
  49        of  mail from worms or viruses; they do not decode attach-
  50        ments, and they do not unzip archives. See  the  documents
  51        referenced  below  in the README FILES section if you need
  52        more sophisticated content analysis.
  53
  54 <b>FILTERS WHILE RECEIVING MAIL</b>
  55        Postfix implements the  following  four  built-in  content
  56        inspection classes while receiving mail:
  57
  58        <b><a href="postconf.5.html#header_checks">header_checks</a></b> (default: empty)
  59               These   are  applied  to  initial  message  headers
  60               (except for the headers  that  are  processed  with
  61               <b><a href="postconf.5.html#mime_header_checks">mime_header_checks</a></b>).
  62
  63        <b><a href="postconf.5.html#mime_header_checks">mime_header_checks</a></b> (default: <b>$<a href="postconf.5.html#header_checks">header_checks</a></b>)
  64               These  are  applied to MIME related message headers
  65               only.
  66
  67               This feature is available in Postfix 2.0 and later.
  68
  69        <b><a href="postconf.5.html#nested_header_checks">nested_header_checks</a></b> (default: <b>$<a href="postconf.5.html#header_checks">header_checks</a></b>)
  70               These  are  applied  to message headers of attached
  71               email messages (except for  the  headers  that  are
  72               processed with <b><a href="postconf.5.html#mime_header_checks">mime_header_checks</a></b>).
  73
  74               This feature is available in Postfix 2.0 and later.
  75
  76        <b><a href="postconf.5.html#body_checks">body_checks</a></b>
  77               These are applied to all other  content,  including
  78               multi-part message boundaries.
  79
  80               With Postfix versions before 2.0, all content after
  81               the initial message headers is treated as body con-
  82               tent.
  83
  84 <b>FILTERS AFTER RECEIVING MAIL</b>
  85        Postfix  supports a subset of the built-in content inspec-
  86        tion classes after the message is received:
  87
  88        <b><a href="postconf.5.html#milter_header_checks">milter_header_checks</a></b> (default: empty)
  89               These are applied to headers that  are  added  with
  90               Milter applications.
  91
  92               This feature is available in Postfix 2.7 and later.
  93
  94 <b>FILTERS WHILE DELIVERING MAIL</b>
  95        Postfix supports all four content inspection classes while
  96        delivering mail via SMTP.
  97
  98        <b><a href="postconf.5.html#smtp_header_checks">smtp_header_checks</a></b> (default: empty)
  99
 100        <b><a href="postconf.5.html#smtp_mime_header_checks">smtp_mime_header_checks</a></b> (default: empty)
 101
 102        <b><a href="postconf.5.html#smtp_nested_header_checks">smtp_nested_header_checks</a></b> (default: empty)
 103
 104        <b><a href="postconf.5.html#smtp_body_checks">smtp_body_checks</a></b> (default: empty)
 105               These  features  are  available  in Postfix 2.5 and
 106               later.
 107
 108 <b>COMPATIBILITY</b>
 109        With Postfix version 2.2 and earlier specify "<b>postmap -fq</b>"
 110        to query a table that contains case sensitive patterns. By
 111        default, <a href="regexp_table.5.html">regexp</a>: and <a href="pcre_table.5.html">pcre</a>: patterns are case  insensitive.
 112
 113 <b>TABLE FORMAT</b>
 114        This  document  assumes  that header and <a href="postconf.5.html#body_checks">body_checks</a> rules
 115        are specified in the form of  Postfix  regular  expression
 116        lookup  tables.  Usually  the best performance is obtained
 117        with <b>pcre</b> (Perl Compatible Regular Expression) tables, but
 118        the  slower  <b>regexp</b> (POSIX regular expressions) support is
 119        more widely available.  Use the command "<b>postconf  -m</b>"  to
 120        find  out what lookup table types your Postfix system sup-
 121        ports.
 122
 123        The general format of Postfix regular expression tables is
 124        given  below.   For  a  discussion  of specific pattern or
 125        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>,
 126        respectively.
 127
 128        <b>/</b><i>pattern</i><b>/</b><i>flags action</i>
 129               When  /<i>pattern</i>/  matches  the input string, execute
 130               the corresponding <i>action</i>. See below for a  list  of
 131               possible actions.
 132
 133        <b>!/</b><i>pattern</i><b>/</b><i>flags action</i>
 134               When  /<i>pattern</i>/  does  <b>not</b>  match the input string,
 135               execute the corresponding <i>action</i>.
 136
 137        <b>if /</b><i>pattern</i><b>/</b><i>flags</i>
 138
 139        <b>endif</b>  Match the input string against the patterns between
 140               <b>if</b>  and <b>endif</b>, if and only if the same input string
 141               also matches /<i>pattern</i>/. The <b>if</b>..<b>endif</b> can nest.
 142
 143               Note: do not prepend whitespace to patterns  inside
 144               <b>if</b>..<b>endif</b>.
 145
 146        <b>if !/</b><i>pattern</i><b>/</b><i>flags</i>
 147
 148        <b>endif</b>  Match the input string against the patterns between
 149               <b>if</b> and <b>endif</b>, if and only if the same input  string
 150               does <b>not</b> match /<i>pattern</i>/. The <b>if</b>..<b>endif</b> can nest.
 151
 152        blank lines and comments
 153               Empty  lines and whitespace-only lines are ignored,
 154               as are lines whose first  non-whitespace  character
 155               is a `#'.
 156
 157        multi-line text
 158               A  pattern/action  line  starts with non-whitespace
 159               text. A line that starts with whitespace  continues
 160               a logical line.
 161
 162 <b>TABLE SEARCH ORDER</b>
 163        For  each  line of message input, the patterns are applied
 164        in the order as specified in the table. When a pattern  is
 165        found  that  matches  the  input  line,  the corresponding
 166        action is  executed  and  then  the  next  input  line  is
 167        inspected.
 168
 169 <b>TEXT SUBSTITUTION</b>
 170        Substitution  of  substrings  from  the matched expression
 171        into the <i>action</i> string is possible using the  conventional
 172        Perl  syntax  (<b>$1</b>,  <b>$2</b>,  etc.).   The macros in the result
 173        string may need to be written as  <b>${n}</b>  or  <b>$(n)</b>  if  they
 174        aren't followed by whitespace.
 175
 176        Note:  since negated patterns (those preceded by <b>!</b>) return
 177        a result when the expression does not match, substitutions
 178        are not available for negated patterns.
 179
 180 <b>ACTIONS</b>
 181        Action names are case insensitive. They are shown in upper
 182        case for consistency with other Postfix documentation.
 183
 184        <b>DISCARD</b> <i>optional text...</i>
 185               Claim successful delivery and silently discard  the
 186               message.   Log the optional text if specified, oth-
 187               erwise log a generic message.
 188
 189               Note:  this  action  disables  further  header   or
 190               <a href="postconf.5.html#body_checks">body_checks</a>  inspection  of the current message and
 191               affects all recipients.  To discard only one recip-
 192               ient without discarding the entire message, use the
 193               <a href="transport.5.html">transport(5)</a> table to direct mail to the <a href="discard.8.html">discard(8)</a>
 194               service.
 195
 196               This feature is available in Postfix 2.0 and later.
 197
 198               This feature is not supported with smtp header/body
 199               checks.
 200
 201        <b>DUNNO</b>  Pretend  that the input line did not match any pat-
 202               tern, and inspect the next input line. This  action
 203               can be used to shorten the table search.
 204
 205               For  backwards  compatibility reasons, Postfix also
 206               accepts <b>OK</b> but it is (and always has been)  treated
 207               as <b>DUNNO</b>.
 208
 209               This feature is available in Postfix 2.1 and later.
 210
 211        <b>FILTER</b> <i>transport:destination</i>
 212               After the message is queued, send the  entire  mes-
 213               sage through the specified external content filter.
 214               The <i>transport</i> name specifies the first field  of  a
 215               mail  delivery  agent  definition in <a href="master.5.html">master.cf</a>; the
 216               syntax of the next-hop <i>destination</i> is described  in
 217               the  manual  page  of  the  corresponding  delivery
 218               agent.  More  information  about  external  content
 219               filters is in the Postfix <a href="FILTER_README.html">FILTER_README</a> file.
 220
 221               Note  1: do not use $<i>number</i> regular expression sub-
 222               stitutions for <i>transport</i> or <i>destination</i> unless  you
 223               know that the information has a trusted origin.
 224
 225               Note  2:  this  action  overrides  the <a href="postconf.5.html">main.cf</a> <b><a href="postconf.5.html#content_filter">con</a>-</b>
 226               <b><a href="postconf.5.html#content_filter">tent_filter</a></b> setting, and affects all recipients  of
 227               the  message.  In  the  case  that  multiple <b>FILTER</b>
 228               actions fire, only the last one is executed.
 229
 230               Note 3: the purpose of the  FILTER  command  is  to
 231               override  message routing.  To override the recipi-
 232               ent's <i>transport</i> but not the  next-hop  <i>destination</i>,
 233               specify  an  empty  filter <i>destination</i> (Postfix 2.7
 234               and later), or specify a <i>transport:destination</i> that
 235               delivers   through  a  different  Postfix  instance
 236               (Postfix 2.6 and earlier). Other options are  using
 237               the  recipient-dependent <b><a href="postconf.5.html#transport_maps">transport_maps</a></b> or the sen-
 238               der-dependent   <b><a href="postconf.5.html#sender_dependent_default_transport_maps">sender_dependent_default_transport</a>-</b>
 239               <b><a href="postconf.5.html#sender_dependent_default_transport_maps">_maps</a></b> features.
 240
 241               This feature is available in Postfix 2.0 and later.
 242
 243               This feature is not supported with smtp header/body
 244               checks.
 245
 246        <b>HOLD</b> <i>optional text...</i>
 247               Arrange  for  the  message to be placed on the <b>hold</b>
 248               queue, and inspect the next input line.   The  mes-
 249               sage  remains  on <b>hold</b> until someone either deletes
 250               it or releases it for delivery.  Log  the  optional
 251               text if specified, otherwise log a generic message.
 252
 253               Mail that is placed on hold can  be  examined  with
 254               the  <a href="postcat.1.html"><b>postcat</b>(1)</a>  command,  and  can be destroyed or
 255               released with the <a href="postsuper.1.html"><b>postsuper</b>(1)</a> command.
 256
 257               Note: use "<b>postsuper -r</b>" to release mail  that  was
 258               kept  on  hold for a significant fraction of <b>$<a href="postconf.5.html#maximal_queue_lifetime">maxi</a>-</b>
 259               <b><a href="postconf.5.html#maximal_queue_lifetime">mal_queue_lifetime</a></b>  or  <b>$<a href="postconf.5.html#bounce_queue_lifetime">bounce_queue_lifetime</a></b>,  or
 260               longer.  Use "<b>postsuper -H</b>" only for mail that will
 261               not expire within a few delivery attempts.
 262
 263               Note: this action affects  all  recipients  of  the
 264               message.
 265
 266               This feature is available in Postfix 2.0 and later.
 267
 268               This feature is not supported with smtp header/body
 269               checks.
 270
 271        <b>IGNORE</b> Delete the current line from the input, and inspect
 272               the next input line.
 273
 274        <b>INFO</b> <i>optional text...</i>
 275               Log an "info:" record with the <i>optional text...</i> (or
 276               log  a  generic  text),  and inspect the next input
 277               line. This action is useful for routine logging  or
 278               for debugging.
 279
 280               This feature is available in Postfix 2.8 and later.
 281
 282        <b>PREPEND</b> <i>text...</i>
 283               Prepend one  line  with  the  specified  text,  and
 284               inspect the next input line.
 285
 286               Notes:
 287
 288               <b>o</b>      The  prepended  text is output on a separate
 289                      line,  immediately  before  the  input  that
 290                      triggered the <b>PREPEND</b> action.
 291
 292               <b>o</b>      The prepended text is not considered part of
 293                      the input  stream:  it  is  not  subject  to
 294                      header/body checks or address rewriting, and
 295                      it does not affect the way that Postfix adds
 296                      missing message headers.
 297
 298               <b>o</b>      When prepending text before a message header
 299                      line, the prepended text must begin  with  a
 300                      valid message header label.
 301
 302               <b>o</b>      This action cannot be used to prepend multi-
 303                      line text.
 304
 305               This feature is available in Postfix 2.1 and later.
 306
 307               This   feature   is   not   supported   with   mil-
 308               ter_header_checks.
 309
 310        <b>REDIRECT</b> <i>user@domain</i>
 311               Write a message redirection request  to  the  queue
 312               file,  and  inspect  the next input line. After the
 313               message is queued, it will be sent to the specified
 314               address instead of the intended recipient(s).
 315
 316               Note:  this action overrides the <b>FILTER</b> action, and
 317               affects all recipients of the message. If  multiple
 318               <b>REDIRECT</b>  actions  fire,  only the last one is exe-
 319               cuted.
 320
 321               This feature is available in Postfix 2.1 and later.
 322
 323               This feature is not supported with smtp header/body
 324               checks.
 325
 326        <b>REPLACE</b> <i>text...</i>
 327               Replace the current line with the  specified  text,
 328               and inspect the next input line.
 329
 330               This feature is available in Postfix 2.2 and later.
 331               The description below applies to Postfix 2.2.2  and
 332               later.
 333
 334               Notes:
 335
 336               <b>o</b>      When  replacing  a  message header line, the
 337                      replacement text must  begin  with  a  valid
 338                      header label.
 339
 340               <b>o</b>      The  replaced text remains part of the input
 341                      stream. Unlike the result from  the  <b>PREPEND</b>
 342                      action,  a  replaced  message  header may be
 343                      subject to address rewriting and may  affect
 344                      the  way  that  Postfix adds missing message
 345                      headers.
 346
 347        <b>REJECT</b> <i>optional text...</i>
 348               Reject the  entire  message.  Reply  with  <i>optional</i>
 349               <i>text...</i> when the optional text is specified, other-
 350               wise reply with a generic error message.
 351
 352               Note:  this  action  disables  further  header   or
 353               <a href="postconf.5.html#body_checks">body_checks</a>  inspection  of the current message and
 354               affects all recipients.
 355
 356               Postfix version 2.3 and later support enhanced sta-
 357               tus codes.  When no code is specified at the begin-
 358               ning of <i>optional text...</i>, Postfix inserts a default
 359               enhanced status code of "5.7.1".
 360
 361               This feature is not supported with smtp header/body
 362               checks.
 363
 364        <b>WARN</b> <i>optional text...</i>
 365               Log a "warning:" record with the  <i>optional  text...</i>
 366               (or log a generic text), and inspect the next input
 367               line. This action is useful for debugging  and  for
 368               testing  a  pattern  before  applying  more drastic
 369               actions.
 370
 371 <b>BUGS</b>
 372        Empty lines never match, because some map types mis-behave
 373        when  given  a zero-length search string.  This limitation
 374        may be removed for regular expression tables in  a  future
 375        release.
 376
 377        Many  people  overlook  the main limitations of header and
 378        <a href="postconf.5.html#body_checks">body_checks</a> rules.
 379
 380        <b>o</b>      These rules operate on one logical  message  header
 381               or one body line at a time. A decision made for one
 382               line is not carried over to the next line.
 383
 384        <b>o</b>      If text in the message body is encoded  (<a href="http://tools.ietf.org/html/rfc2045">RFC  2045</a>)
 385               then the rules need to be specified for the encoded
 386               form.
 387
 388        <b>o</b>      Likewise, when message  headers  are  encoded  (<a href="http://tools.ietf.org/html/rfc2047">RFC</a>
 389               <a href="http://tools.ietf.org/html/rfc2047">2047</a>)  then  the rules need to be specified for the
 390               encoded form.
 391
 392        Message headers added by the <a href="cleanup.8.html"><b>cleanup</b>(8)</a> daemon itself  are
 393        excluded from inspection. Examples of such message headers
 394        are <b>From:</b>, <b>To:</b>, <b>Message-ID:</b>, <b>Date:</b>.
 395
 396        Message headers deleted by the <a href="cleanup.8.html"><b>cleanup</b>(8)</a> daemon  will  be
 397        examined before they are deleted. Examples are: <b>Bcc:, Con-</b>
 398        <b>tent-Length:</b>, <b>Return-Path:</b>.
 399
 400 <b>CONFIGURATION PARAMETERS</b>
 401        <b><a href="postconf.5.html#body_checks">body_checks</a></b>
 402               Lookup tables with content filter rules for message
 403               body lines.  These filters see one physical line at
 404               a time, in chunks  of  at  most  <b>$<a href="postconf.5.html#line_length_limit">line_length_limit</a></b>
 405               bytes.
 406
 407        <b><a href="postconf.5.html#body_checks_size_limit">body_checks_size_limit</a></b>
 408               The  amount  of  content  per  message body segment
 409               (attachment) that is subjected to <b>$<a href="postconf.5.html#body_checks">body_checks</a></b> fil-
 410               tering.
 411
 412        <b><a href="postconf.5.html#header_checks">header_checks</a></b>
 413
 414        <b><a href="postconf.5.html#mime_header_checks">mime_header_checks</a></b> (default: <b>$<a href="postconf.5.html#header_checks">header_checks</a></b>)
 415
 416        <b><a href="postconf.5.html#nested_header_checks">nested_header_checks</a></b> (default: <b>$<a href="postconf.5.html#header_checks">header_checks</a></b>)
 417               Lookup tables with content filter rules for message
 418               header lines: respectively, these  are  applied  to
 419               the  initial  message  headers  (not including MIME
 420               headers), to the MIME headers anywhere in the  mes-
 421               sage,  and  to the initial headers of attached mes-
 422               sages.
 423
 424               Note: these filters see one logical message  header
 425               at  a time, even when a message header spans multi-
 426               ple lines. Message headers  that  are  longer  than
 427               <b>$<a href="postconf.5.html#header_size_limit">header_size_limit</a></b> characters are truncated.
 428
 429        <b><a href="postconf.5.html#disable_mime_input_processing">disable_mime_input_processing</a></b>
 430               While  receiving mail, give no special treatment to
 431               MIME related message headers; all  text  after  the
 432               initial message headers is considered to be part of
 433               the message body. This means that <b><a href="postconf.5.html#header_checks">header_checks</a></b>  is
 434               applied  to  all  the  initial message headers, and
 435               that <b><a href="postconf.5.html#body_checks">body_checks</a></b> is applied to the remainder of the
 436               message.
 437
 438               Note:  when  used  in this manner, <b><a href="postconf.5.html#body_checks">body_checks</a></b> will
 439               process a multi-line message header one line  at  a
 440               time.
 441
 442 <b>EXAMPLES</b>
 443        Header  pattern  to  block  attachments with bad file name
 444        extensions.  For convenience, the PCRE /x flag  is  speci-
 445        fied,  so  that  there  is no need to collapse the pattern
 446        into  a  single  line  of  text.   The  purpose   of   the
 447        [[:xdigit:]] sub-expressions is to recognize Windows CLSID
 448        strings.
 449
 450        /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 451            <a href="postconf.5.html#header_checks">header_checks</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/header_checks.pcre
 452
 453        /etc/postfix/header_checks.<a href="pcre_table.5.html">pcre</a>:
 454            /^Content-(Disposition|Type).*name\s*=\s*"?(.*(\.|=2E)(
 455              ade|adp|asp|bas|bat|chm|cmd|com|cpl|crt|dll|exe|
 456              hlp|ht[at]|
 457              inf|ins|isp|jse?|lnk|md[betw]|ms[cipt]|nws|
 458              \{[[:xdigit:]]{8}(?:-[[:xdigit:]]{4}){3}-[[:xdigit:]]{12}\}|
 459              ops|pcd|pif|prf|reg|sc[frt]|sh[bsm]|swf|
 460              vb[esx]?|vxd|ws[cfh]))(\?=)?"?\s*(;|$)/x
 461                REJECT Attachment name "$2" may not end with ".$4"
 462
 463        Body pattern to stop a specific HTML browser vulnerability
 464        exploit.
 465
 466        /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 467            <a href="postconf.5.html#body_checks">body_checks</a> = <a href="regexp_table.5.html">regexp</a>:/etc/postfix/body_checks
 468
 469        /etc/postfix/body_checks:
 470            /^&lt;iframe src=(3D)?cid:.* height=(3D)?0 width=(3D)?0&gt;$/
 471                REJECT IFRAME vulnerability exploit
 472
 473 <b>SEE ALSO</b>
 474        <a href="cleanup.8.html">cleanup(8)</a>, canonicalize and enqueue Postfix message
 475        <a href="pcre_table.5.html">pcre_table(5)</a>, format of PCRE lookup tables
 476        <a href="regexp_table.5.html">regexp_table(5)</a>, format of POSIX regular expression tables
 477        <a href="postconf.1.html">postconf(1)</a>, Postfix configuration utility
 478        <a href="postmap.1.html">postmap(1)</a>, Postfix lookup table management
 479        <a href="postsuper.1.html">postsuper(1)</a>, Postfix janitor
 480        <a href="postcat.1.html">postcat(1)</a>, show Postfix queue file contents
 481        <a href="http://tools.ietf.org/html/rfc2045">RFC 2045</a>, base64 and quoted-printable encoding rules
 482        <a href="http://tools.ietf.org/html/rfc2047">RFC 2047</a>, message header encoding for non-ASCII text
 483
 484 <b>README FILES</b>
 485        <a href="DATABASE_README.html">DATABASE_README</a>, Postfix lookup table overview
 486        <a href="CONTENT_INSPECTION_README.html">CONTENT_INSPECTION_README</a>, Postfix content inspection overview
 487        <a href="BUILTIN_FILTER_README.html">BUILTIN_FILTER_README</a>, Postfix built-in content inspection
 488        <a href="BACKSCATTER_README.html">BACKSCATTER_README</a>, blocking returned forged mail
 489
 490 <b>LICENSE</b>
 491        The Secure Mailer license must be  distributed  with  this
 492        software.
 493
 494 <b>AUTHOR(S)</b>
 495        Wietse Venema
 496        IBM T.J. Watson Research
 497        P.O. Box 704
 498        Yorktown Heights, NY 10598, USA
 499
 500                                                               HEADER_CHECKS(5)
 501 </pre> </body> </html>