Swaks - Swiss Army Knife for SMTP
Swaks is a featureful, flexible, scriptable, transaction-oriented SMTP test tool written and maintained by John Jetmore.
Currently Swaks is hosted in a private svn repository. I am creating this github repository to give Swaks some sort of official presence on github.
The official project page is http://jetmore.org/john/code/swaks/
There is also a versions page which lists every released version of Swaks, complete with changelogs and download links.