What is the Sender Rewriting Scheme (SRS) in Email?


Sender Rewriting Scheme (SRS) is a process that rewrite the sender address:

[email protected]


[email protected]

It is mandatory in order to conform to the SPF scheme when the emails are forwarded.

With SRS, an MTA can circumvent SPF restrictions by replacing the envelope sender with a temporary email address from one of their own domains.

This temporary address is:

  • bound to the original sender
  • and only valid for a certain amount of time, which prevents abuse by spammers.


If you get a forwarded email with SRS, you should see:

  • the email rewrite
  • the added Return Path
  • a successful SPF test

Example from Gmail

Postsrsd Spf Pass




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Postsrsd Spf Pass
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