I thought this was pretty handy, originally from here
This is gonna be like a small info bulletin on how attachments are sent.
This work is copyright � 2000 Philip S Tellis
This work is licensed under a Creative Commons License:
http://creativecommons.org/licenses/by-nc-sa/2.0/
When you send mail using the SMTP protocol, you basically have only the
following commands:
HELO [...]