manually create a ~/.procmail file for each user, or users can create their
own.
There is no system-wide 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. Ubuntu 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. You can find details for the rulesets in the man page for Procmail
and in 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 sent to thousands of people at the same time.
Ubuntu 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 system-wide and individual use. It uses 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 in
/usr/share/doc/spamassasin provides details on configuring the
.procmail file to process mail through Spamassassin. Spamassassin tags
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 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 ones used by Gmail, Hotmail, or Yahoo! Mail. Ubuntu
provides Squirrelmail for just that purpose. Squirrelmail, which is written in
PHP, supports IMAP and SMTP. It supports MIME attachments and an