RFC 1123 introduced two very convenient but easily abused features: relaying without regard to recipient (open relays) and forwarding without regard to sender. Both features have been abused to the point of unusability. Open relays have been suppressed via blacklisting. SPF stops forwarding without rewriting, but it does so on an opt-in basis. If you, as a recipient do not check SPF, then you can continue to use forwarding without rewriting the sender as before. However, if you do check SPF, and you wish to reject messages that fail SPF, then you must do one of two things to avoid rejecting legitimate mail.
| | RFC 1123 introduced two very convenient but easily abused features: relaying without regard to recipient (open relays) and forwarding without regard to sender. Both features have been abused to the point of unusability. Open relays have been suppressed via blacklisting. SPF stops forwarding without rewriting, but it does so on an opt-in basis. If you, as a recipient do not check SPF, then you can continue to use forwarding without rewriting the sender as before. However, if you do check SPF, and you wish to reject messages that fail SPF, then you must do one of two things to avoid rejecting legitimate mail:
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SPF "breaks" email forwarding. SRS is a way to fix it. SRS is a simple way for forwarding MTAs to rewrite the sender address. The original concept was published in [[http://www.openspf.org/svn/project/specs/drafts/draft-mengwong-sender-rewrite-01.txt|draft-mengwong-sender-rewrite]].
| | SPF "breaks" email forwarding. SRS is a way to fix it. SRS is a simple way for forwarding MTAs to rewrite the sender address. The original concept was published in [[http://www.openspf.org/svn/project/specs/drafts/draft-mengwong-sender-rewrite-01.txt|draft-mengwong-sender-rewrite]] and further expanded on in a [[http://www.libsrs2.org/srs/srs.pdf|paper by Shevek]].
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