This package contains a sendmail binary version 8.12.4 compiled for MacOS X. Contrary to Apple's current (as of MacOS X 10.1.5) version, it has client authentication functionality built in. This is important if you want to forward all your outgoing mails to the SMTP server of your ISP (instead of delivering them directly), and this STMP server requires authentication (which becomes more and more common as a means of spam protection).
NOTE: To keep the installation simple, this binary has only *client* side authentication built in. This means that your sendmail mail server will be able to forward mails to a smart relay host that requires authentication. It will *not* be able to require authentication itself to accept mails.
ALSO NOTE: The binary only supports the AUTH PLAIN authentication mechanism, simply because that's all 99.9% of the ISPs seem to use right now. Be aware that this mechanism is not really secure, since your user name and password will be sent across the Internet only base64 "encrypted", which is little more than "not encrypted at all".