How to reject SMTP send if From header doesn't match SMTP user?

Manoa R.

• November 16, 2020 03:21

Good morning, As the title says, How to reject SMTP send if From header doesn't match SMTP user? Concretely, I want to disallow user1@domain.com to send emails with "From: user2@domain.com" in the header. Thanks in advance.

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  keat63

  • November 16, 2020 13:41

  I'l be honest, I'm not entirely sure that this is possible. I'm pretty sure it's been discussed on here many times, although I could be wrong. You could look in exim config at: EXPERIMENTAL: Rewrite From: header to match actual sender

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  cPRex Jurassic Moderator

  • November 16, 2020 15:16

  I think this is similar to the many "how to stop spoofing" threads that get created. You can't really prevent then with 100% certainty, but there are things you can do to help reduce the chances of them getting through. A few possible options are here:

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  Manoa R.

  • November 17, 2020 09:27

  Hello, After a lot of searching, I decided to filter these email using Exim filter. So, I added /usr/local/cpanel/etc/exim/sysfilter/options/fail_from_dont_match_sender
  with the following content: if $header_from: does not matches "" and $header_from: does not contains $sender_address then fail text "From header doesn't match authenticated sender" seen finish endif
  I applied changes by enabling this filter on WHM > Service Configuration > Exim Configuration Manager but it doesn't work. I did something wrong?

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  WasChristine

  • November 17, 2020 13:45

  Hello. Does adjusting this line make any changes to the way that your filter works?: if $header_from: does not matches "" and
  Specifically changing "matches" to "match". We must note that our assistance on this matter is quite limited, though you may be able to get this to work through testing various changes in the custom filter.

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