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 example.com
(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 - http://www.openspf.org/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 "yourdomain.com" 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/main.cf):
canonical_maps = pcre:/etc/postfix/canonical
canonical_classes = envelope_sender
- Map the new changes into Postfix compatibility:
- Reload the Postfix configuration:
This will envelope all external emails with email@example.com, which will be accepted by SpamHero.