SRS (Sender Rewriting Scheme)
SRS (Sender Rewriting Scheme) fixes SPF failures caused by email forwarding by rewriting the envelope sender address at the forwarding server, replacing it with an address on the forwarder's own domain that still encodes the original sender for bounce routing. Because SPF checks the connecting server's IP against the domain in the, now rewritten, envelope sender, and that address belongs to the forwarder, it's the forwarder's own SPF record -- which correctly lists its own IP -- that gets checked, so the forwarded message passes instead of failing on the original domain's SPF record, which never authorized the forwarder. SRS is a widely implemented convention rather than a formal IETF standard; it only works if the forwarding server itself supports it, and it does nothing for DKIM, which a message-modifying forwarder can still break separately.
By AdminKit team, Netbase JSC · Updated