Aha. Yes, it looks like this is the way forward! After a quick google I came across http://www.libsrs2.org/ which provides some additional details. Cheers! Spencer. Craig Whitmore said:
One of our user domains has just been heavily hit by *huge* quantities of Non-Delivery Receipts addressed to random_string(a)domain_name.
Something like this can be stopped using SRS with SPF. If the messages are bounced back and it doesn't have SRS then it will be rejected. People who have SPF will reject in the 1st instance (as the messages won't be coming from the corect place) and your server will reject in the 2nd instance if bounced back with invalid/no SRS.
Thanks Craig http://www.spam.co.nz
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