We have changed the way our SRS:Sender Rewriting Scheme system works.

Previously all messages sent out via our mail server have been subject to SRS. This has caused a few isolated problems. Namely message bounces because of whitelist mis-matches and problems with receivers who operate sender verification systems.

To resolve this we now only perform SRS on forwarded mail. So if the email is sent via SMTP Auth or uses a from address hosted on our system we will not perform SRS. But if the message is received by us then forwarded to an external mailbox then we will perform SRS to ensure SPF compliance.

There is a downside to this change in implementation. The Bounce Attack Prevention method previously provided will no longer work. Instead you will have to block all bounce emails. We will be updating the support article shortly.

However our mail system is now much more sophisticated and much better at dealing with such attacks automatically.