Choosing a Mail Delivery Agent

Because of the modular nature of mail handling, it is possible to use multiple applications to process mail and accomplish more than simply deliver it. Getting mail from the storage area and displaying it to the user is the purpose of the mail delivery agent (MDA). MDA functionality can be found in some of the mail clients (MUAs), which can cause some confusion to those still unfamiliar with the concept of Unix mail. As an example, the Procmail MDA provide filtering based on rulesets; KMail and Evolution, both MUAs, provide filtering, but the MUAs pine, mutt, and Balsa do not. Some MDAs perform simple sorting, and other MDAs are designed to eliminate unwanted emails, such as spam and viruses.

You would choose an MDA based on what you want to do with your mail. We'll look at five MDAs that offer functions you might find useful in your particular situation. If you have simple needs (just organizing mail by rules), one of the MUAs that offers filtering might be better for your needs. Fedora provides the Evolution MUA as the default selection (and it contains some MDA functionality as previously noted), so try that first and see if it meets your needs. If not, investigate one of the following MDAs provided by Fedora.

Unless otherwise noted, all the MDA software is provided with the Fedora discs. Chapter 7 details the general installation of any software.

Procmail

As a tool for advanced users, the Procmail application acts as a filter for email as it is retrieved from a mail server. It uses rulesets (known as recipes) as it reads each email message. No default configuration is provided; you must manually create a ~/.procmail file for each user, or each user can create her own.

There is no systemwide default configuration file. The creation of the rulesets is not trivial and requires an understanding of the use of regular expressions that is beyond the scope of this chapter. Fedora Core does provide three examples of the files in /usr/share/doc/procmail/examples, as well as a fully commented example in the /usr/share/doc/procmail directory, which also contains a README and FAQ. Details for the rulesets can be found in the man page for Procmail as well as the man pages for procmailrc, procmailsc, and procmailex, which contain examples of Procmail recipes.

Spamassassin

If you have used email for any length of time, you have likely been subjected to spam unwanted email that is sent to thousands of people at the same time. Fedora provides an MDA named Spamassassin to assist you in reducing and eliminating unwanted emails. Easily integrated with Procmail and Sendmail, it can be configured for both systemwide and individual use. It employs a combination of rulesets and blacklists (Internet domains known to mail spam).

Enabling Spamassassin is simple. You must first have installed and configured Procmail. The README file found in /usr/share/doc/spamassasin provides details on configuring the .procmail file to process mail through Spamassassin. It will tag probable spam with a unique header; you can then have Procmail filter the mail in any manner you choose. One interesting use of Spamassasin is to use it to tag email received at special email accounts established solely for the purpose of attracting spam. This information is then shared with the Spamassassin site where these "spam trap" generated hits help the authors fine-tune the rulesets.

Squirrelmail

Perhaps you do not want to read your mail in an MUA. If you use your web browser often, it might make sense to read and send your mail via a web interface, such as the one used by Hotmail or Yahoo! mail. Fedora provides Squirrelmail for just that purpose. Squirrelmail is written in the PHP 4 language and supports IMAP and SMTP with all pages rendering in HTML 4.0 without using Java. It supports MIME attachments, as well as an address book and folders for segregating email.

You must configure your web server to work with PHP 4. Detailed installation instructions can be found in /usr/share/doc/squirrelmail/INSTALL. Once configured, point your web browser to http://www.yourdomain.com/squirellmail/ to read and send email.

Virus Scanners

Although the currently held belief is that Linux is immune to email viruses targeted at Microsoft Outlook users, it certainly makes no sense for Unix mail servers to permit infected email to be sent through them. Although Fedora does not provide a virus scanner, one of the more popular of many such scanners is MailScanner, available from http://www.sng.ecs.soton.ac.uk/mailscanner/; a Fedora RPM package is available as well as the source code. It supports Sendmail and Exim, but not Postfix or Qmail. Searching on the terms "virus" and "email" at Freshmeat.net will turn up a surprising list of GPLed virus scanners that might serve your needs.

Special Mail Delivery Agents

If you already use Hotmail or another web-based email account, the currently available MUAs will not be useful to you; formal POP3 access to a Hotmail account is not available free of charge. However, Microsoft Outlook Express can access Hotmail at no charge using a special protocol called HTTPMail. How that is done is covered in RFC-2518 as "WebDAV extensions to HTTP/1.1." No specific solution is provided by Fedora, but the basic tools it provides are adequate when supplemented by some clever Perl programming.

Hotwayd is available from http://sourceforge.net/projects/hotwayd/ and implements this functionality, allowing you to use your favorite mail client to read mail from Hotmail.

A newer Hotmail access tool is Gotmail from http://sourceforge.net/projects/gotmail. It is a Perl script that is easy to configure. There are brief tutorials on configuring it for use with KMail and Evolution at http://www.madpenguin.org/cms/?m=show&id=437.

A similar tool exists for Yahoo! mail. FetchYahoo is available from http://fetchyahoo.twizzler.org/.

Once implemented, you can use a regular MUA, or mail client, to access your web-based mail. None of them, however, enable you to send mail through Hotmail or Yahoo! mail.