SRS email address rewriting engine
libsrs2 is the next generation SRS library. SPF verifies that the Sender address of a mail matches (according to some policy) the client IP address which submits the mail. When a mail is forwarded, the sender address must be rewritten to comply with SPF policy. The Sender Rewriting Scheme, or SRS, provides a standard for this rewriting which is not vulnerable to attacks by spammers.