libsrs2 is the next generation Sender Rewriting Scheme (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 SRS provides a standard
for this rewriting which is not vulnerable to attacks by spammers.

1. build dependencies:
   1. chrpath
   2. gcc-c++