Sender Policy Framework

When SPF was first deployed it was necessary to directly patch mail servers to enable SPF checking. Currently all major MTAs either offer native SPF checking (e.g. Exim and Courier) or have defined interfaces through which SPF checking can be performed (e.g. Sendmail with milters and Postfix with policy servers or milters).

Direct patching of the internals of MTA programs is a poor software engineering practice and should be avoided whenever possible. With the exception of Qmail, direct patching of major MTA progams is no longer Necessary.