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I use Postfix to block terms in headers and bodies. In few cases, it blocks legitimate mails because the term used is present in a long string (probably an id or reference or a coded string).

For example:

/AQHV/ REJECT SPAM RULE #5

Emails containing the following text in their headers are rejected. Because the characters "AQHV" are in the one of the headers:-

Thread-Index: AQHVSEXnJ2u6futfzU6u85aNv7EgTg

I have tried to add a space before + after the term AQHV, like so:-

/ AQHV/ REJECT SPAM RULE #5

/AQHV / REJECT SPAM RULE #6

This error occurs:

postmap: warning: /etc/postfix/header_checks.db: duplicate entry: "/"

How can I tell Postfix to treat the term "AQHV" as a separate word only, and not as part of a string?

Thanks in advance!

tripleee: apologies for the comments - still struggling with these forums.

I have decided to uninstall Postfix and reinstall it again. It might solve this problem. I will accept your answer. Many thanks.

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  • The error message sounds vaguely like you put these in the wrong file or something. Can you show how you have configured this db?
    – tripleee
    Commented Aug 1, 2019 at 14:35
  • They are put in /etc/postfix/header_checks file. Then: # postmap /etc/postfix/header_checks # service postfix restart
    – Quest
    Commented Aug 1, 2019 at 16:44

2 Answers 2

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Try /\bAHQV\b/. Here \b is a regex word boundary marker.

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  • Thank you for your response. This /\bAQHV\b/ hasn't worked for me. Tested an email with subject AQHV and it was not rejected. I am not using regex. As explained in the post, they are just terms followed by REJECT
    – Quest
    Commented Aug 1, 2019 at 16:46
  • Correction: I meant /\AQHV\b/ hasn't worked for me. The previous one was a typo
    – Quest
    Commented Aug 1, 2019 at 16:54
  • Then switch to regexp, or probably preferably the pcre filter type. The syntax with slashes is specific to the regex filters.
    – tripleee
    Commented Aug 1, 2019 at 16:57
  • The 2 lines were already added to main.cf:- header_checks = pcre:/etc/postfix/header_checks body_checks = pcre:/etc/postfix/body_checks Please point me in the right direction!
    – Quest
    Commented Aug 1, 2019 at 17:03
  • Just to add that the command: postconf -m shows that both pcre + regexp are installed.
    – Quest
    Commented Aug 1, 2019 at 17:21
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Make sure you include this in main.cf:

header_checks = pcre:/etc/postfix/header_checks

Run these commands, assuming header_checks is in /etc/postfix/.

postmap /etc/postfix/header_checks
postfix reload

To deal with spaces in regex/pcre, you can comment them out. For example, if you wanted to reject any email with a space in the header, you could put this in header_checks:

/\ / REJECT NO SPACES ALLOWED!!!!

So, if you wanted to just block an email with a line in the header that contained AHQV, but just the string AHQV, not AHQV as a substring in a larger string, then this is the regex you need:

/\ AHQV\ / REJECT NO AHQV PLS

I hope this helps!!

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