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If you are seeing one of the following error messages while using Postfix with our Outbound filtering service, then this article may help you:

"Envelope Sender Blank, check Header From instead"
"Sender domain is either not active, subscribed, or currently not allowed to forward"

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 March 28, 2019