man procmailrc

If the regular expression contains ^TO_' it will be substituted by (^((Ori
ginal-)?(Resent-)?(To|Cc|Bcc)|(X-Envelope|Apparently(-Resent)?)-To):(.*[^-a-zA

• Z0-9_.])?)', which should catch all destination specifications containing a
  specific address. If the regular expression contains ^TO' it will be substituted by (^((Original-)?(Resent-)?(To|Cc|Bcc)|(X-Envelope|Apparently(-R
  esent)?)-To):(.[^a-zA- Z])?)', which should catch all destination
  specifications containing a specific word. If the regular expression contains
  ^FROM_DAEMON' it will be substituted by (^(Mailing-
  List:|Precedence:.(junk|bulk|list)|To: Multiple recipients of
  |(((Resent-)?(From|Sender) |X-Envelope-From):|>?From
  )([^>][^(.%@a-z0-9])?(Post(ma?(st(e?r)?|n)|office) |(send)?Mail(er)?|daemon|m
  (mdf|ajordomo)|n?uucp|LIST(SERV|proc)|NETSERV|o(wner|ps) |r(e(quest|sponse)|oo
  t)|b(ounce|bs.smtp)|echo|mirror|s(erv(ices?|er)|mtp(error)?|ystem)
  |A(dmin(istrator)?|MMGR|utoanswer))(([^).!:a-z0-9][-_a-z0-9])?[%@>\t
  ][^<)]((.).)?)?$([^>]|$)))', which should catch mails coming from most
  daemons (how's that for a regular expression :-). If the regular expression
  contains ^FROM_MAILER' it will be substituted by (^(((Resent-)?(From|Sender)|X-Envelope-From):|>?From )([^>][^(.%@a- z0-9])?(
  Post(ma(st(er)?|n)|office)|(send)?Mail(er)?|daemon|mmdf|n?uucp|ops|r(esponse|o
  ot) |(bbs.)?smtp(error)?|s(erv(ices?|er)|ystem)|A(dmin(istrator)?|MMGR))(([^)
  .!:a-z0-9][-_a- z0-9])?[%@>\t ][^<)]((.).)?)?$([^>]|$))' (a stripped
  down version of `^FROM_DAEMON'), which should catch mails coming from most
  mailer-daemons.

( link ) ziemlich
sinnvolle regex um übersichtliche procmail dateien zu bauen ...

{% include JB/setup %}