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If you are seeing one of the following error, then this article may help:

550 5.7.1 Cannot forward message. To forward mail "From" an external domain, the Return-Path (or recipient) must belong to (or a related domain aliases)

If you are using Postfix with our Outbound filtering system, and you need to forward your incoming messages, you may need to enable Sender Rewriting Scheme (SRS - for these forwards.  This will cause the messages being forwarded to use your domain name, so our outbound filter will allow the messages to pass.


  • Ensure you have PCRE support installed for Postfix:
sudo apt-install postfix-pcre
  • Create and edit a file which will contain the regular expression for changing the sender address:
sudo vi /etc/postfix/canonical
  • Add this line to the new file, but replace "" with your actual domain (this must be either subscribed or aliased on your SpamHero account):

  • Then connect this new file to your Postfix configuration (edit /etc/postfix/
canonical_maps = pcre:/etc/postfix/canonical
canonical_classes = envelope_sender
  • Map the new changes into Postfix compatibility:
postmap pcre:/etc/postfix/canonical
  • Reload the Postfix configuration:
postfix reload

This will envelope all external emails with, which will be accepted by SpamHero.

Last updated November 2, 2022