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Playing with postfix check_headers directive

Application: Postfix
Version: 2.9
System: Debian
Description:
Use check_headers to replace some headers from emails send by postfix

Basics:

• settings in main.conf:
  • header_checks = regexp:/etc/postfix/header_check
    Meaning: regexp is one of the methods
• file header_check:
• /(.*)(something)/ REPLACE $1
  Meaning: will find "something" and replace it with $1=(.*)[everything before], it means deletion of "something"

  /^(Received: from somehost)(.*)/ REPLACE X-$1$2
  Meaning: will match (everything in bracket) eg $1 and replace it with X-$1[X-Received: from somehost] and append the rest of the header

  /^Received: from 127.0.0.1/ IGNORE

  /^Received: from localhost/ IGNORE

  /(.*)(..\(This is the line from multiline header\))(.*)/ REPLACE $1$3
  Meaning: will add strings before, $2=[can be second line for example] replace with nothing and append the rest BEWARE of .. which is needed to have proper header format otherwise you can received BAD HEADER and ur mgs can be discarted