Do you support SRS (Sender Rewriting Scheme)?

Explains how ImprovMX supports a custom implementation of SRS (Sender Rewriting Scheme) that ensures emails forwarded through ImprovMX pass SPF checks.

About SRS

SRS, or Sender Rewriting Scheme (whitepaper) is a mechanism designed to make email forwarding compatible with modern SPF (Sender Policy Framework) checks. SPF verifies that incoming mail from a domain comes from a server authorized by that domain’s administrators. But forwarding breaks SPF, because when a message gets forwarded, the receiving mail server sees the forwarder's IP instead of the original sender’s—causing SPF to fail.

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SRS and ImprovMX

At ImprovMX, we care deeply about ensuring forwarded emails are delivered reliably. That’s why we implement our own custom version of SRS behind the scenes.

Instead of using a generic SRS library, we rewrite the envelope sender (Return-Path) to a special address at a domain we control. When your mail is forwarded through us, this rewritten Return-Path ensures that SPF checks pass at the recipient’s mail server. This helps prevent your forwarded messages from being flagged as spam or rejected entirely.

We also store metadata about each rewritten email, so if we receive a bounce or delivery error, we can trace it back to the original sender. This gives us the benefits of SRS while maintaining control over delivery quality and diagnostics.

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In short: SRS helps fix SPF for forwarded emails, and our custom SRS implementation is one of the reasons your messages arrive where they’re supposed to.

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