Hi Lennart. Perhaps the auto-response is sent back, but it is sent back to the antispam gateway and not the actual sender of the email. Have you checked your delivery log to see if the auto-responses are being sent at all? If you see that they are being sent, check to see who they are being sent to. If it's the gateway, you can then contact SpamTitan to see how to resolve this. I hope this points you in the right direction. Thanks! :)

Have you checked the domains settings in smartermail to make sure that it allows auto responders for all spam scores?

Thanks for your answers.

I have changed settings to allow auto responders for all spam scores for the entire domain.

I checked the delivery log and there is not sent any mail.
When I send from our own domain on the same server I can see the reply in the log.

When I check the header of the received mail it shows correct From address and also correct Return-Path.

Logfile:

That's all. No reply.