We are please to announce that SRS:Sender Rewriting Scheme is now perfomed by all AGUK outgoing mail servers.

SRS is a method used to rewrite the return-path header of outgoing messages. The reason for it’s importance is that is ensures SPF and sender checks are not broken when mail is forwarded by our servers.

This is necessary when a customer hosts their email domain with AGUK but then forwards the mail on to another email address such as an AOL account.

Here is an example of why this can be a problem.

user@nonagukdomain.com sends mail to you@youragukdomain.com (an email account you host with AGUK). This account then forwards to you@aol.com so we accept the message and then forward it on.

The original sender does not know the mail has been forwarded. When AOL receives the message they perform a number of checks as part of their spam filtering. One of these checks may highlight that our mailserver is not permitted to send mail for user@nonagukdomain.com and as a result they could reject the mail and even blacklist our mailservers.

Now with SRS we rewrite the return-path using a special hashing technique thereby informing AOL that the message has been accepted and then forwarded by us to them and as such the message is more likely to pass the relevant checks.

We have used AOL as an example but the same applies for the majority of ISPs and mailservers.

The implementation of SRS should mean that forwareded mail is handled quicker and more reliably than before.

You can see a diagram explaining SRS in more detail here

We have also published a couple of KB articles on SRS.

• Q10127 - FAQ: Do you utilise SRS: Sender Rewriting Scheme?
• Q10126 - FAQ: Why do I receive mail from an extremely long email address I do not recognise?