Жіберуші мекенжайын өзгерту схемасы (SRS)

Rewriting an email message sender address
The Sender Rewriting Scheme (SRS) is a scheme for bypassing the Sender Policy Framework's (SPF) methods of preventing forged sender addresses. Forging a sender address is also known as email spoofing.

In a number of cases, including change of email address and mailing lists, a message transfer agent (MTA) accepts an email message that is not destined to a local mailbox but needs to be forwarded. In such cases, the question arises of who deserves to receive any related bounce message. In general, that is either the author, or a person or other entity who administers the forwarding itself. Sending bounces to the author is administratively simpler and used to be accomplished by just keeping the original envelope sender. However, if the author address is subject to a strict SPF policy and the target MTA happens to enforce it, the forwarding transaction can be rejected. As a workaround, it is possible to synthesize a temporary bounce address on the fly that will direct any bounce back to the current MTA. The scheme provides a way to recover the original envelope address so that if a bounce does arrive, it can be forwarded along the reverse path, but this time with an empty envelope sender. While there are other workarounds, SRS is a fairly general one. Its notion of reversing the path resembles the original routing dispositions for email, see below. Please note: Using SRS protocol fails the SPF Alignment check for your DMARC record, and it's by design. Your DMARC record can still pass with a DKIM check.

Using a database can definitely control the growth of rewritten addresses, since it is sufficient to put just a unique key in the rewritten local part. It also allows for a certain amount of anonymity in the resending process, if this is desired. However, a database requires centralization and is a single point of failure.

Another possibility is to store the long rewritten address somewhere in the message header. The = tag of a DKIM Signature may be a good place, as such choice considerably improves the security. This technique has been just observed. Unless there is a backup mechanism, it can only work if the bounce message is in a standard format.