If you're interested in exploring the Request For Comment (RFC) documents that describe many of the conventions used in Unix and the Internet, try exploring http://pubweb.nexor.co.uk/public/rfc/index/rfc.html. I used Yahoo (http://www.yahoo.com/) to search for “RFC” and found several sites with varying search capabilities containing the RFC documents. There are several documents on the Simple Mail Transfer Protocol (SMTP), the standard for Internet mail transport. You might want to start with RFC-821, the SMTP specification document from Jonathan B. Postel.
For more information on bash(1), the GNU Bourne-Again Shell, reference the on-line man page.
Procmail, a “versatile e-mail processor” provides powerful mail-handling capabilities. The Debian GNU/Linux 1.2 distribution includes version 3.10-4 of this package. Procmail can serve as a general-purpose mail filter or perform more specialized actions (such as my use of formail). For more information on using procmail or where to find a recent version (if your Linux distribution doesn't include it), visit one of the Linux archive sites (such as ftp://tsx-11.mit.edu/).
I use the Debian GNU/Linux 1.2 distribution, which comes with the version 2.0.27 Linux kernel. For more information on Debian, including where to download it for free and where to obtain it on CD-ROM, visit http://www.debian.org/. Debian has a sophisticated package handling system that makes installation fairly painless. It can also handle Red Hat and Slackware packages.