The biggest advantage if Citadel is ease of installation and ease of configuration. Both of these can be a serious hassle when you are building a Postfix mail server from scratch. So the focus of this documentation is clear easy configuration. The goal also requires a mail server that has an easy interface to make changes with and that is intuitive.

There is currently a lot of spam where the spam "information" is attached as .pdf or .xls files, sometime also hidden inside a .zip file. While these spam mails are not easy to catch with e.g. SpamAssassin or a Bayes filter, the ClamAV virus scanner can catch them easily when it is fed with the correct signatures as ClamAV is built to scan mail attachments.

Spam is a plague on the Internet. It’s constant and unending. Some ISPs and free web mail providers offer anti-spam services but if you’re running your own mail server, accepting mail to your own domain, you have to work out your own solution. Can open source compete with the big boys? When it comes to spam, is there a free lunch?

Although SMTP blocking of e-mail spam is a best practice, many anti-virus products include the dangerous option of blocking when a Received header is on a blacklist. But it is possible for a legitimate, secure system to have its e-mail blocked by this boneheaded technique. Do not use it!

Estimates say that spam makes now up for 80 - 90% of all emails, and many mail servers have difficulties in managing the additional load caused by the latest spam, and spam filters such as SpamAssassin do not recognize large parts of that spam as they did before.

Apache SpamAssassin is an extensible email filter that is used to identify spam. Once identified, the mail can then be optionally tagged as spam for later filtering. It provides a command line tool to perform filtering, a client-server system to filter large volumes of mail, and Mail::SpamAssassin, a set of Perl modules allowing Apache SpamAssassin to be used in a wide variety of email systems.

This guide explains how to install Maia Mailguard, a spam and virus management system, on a Debian Lenny mailserver. Maia Mailguard is a web-based interface and management system based on the popular amavisd-new email scanner and SpamAssassin.

"I run a Postfix-based mail server that services a few hundred users with an average load of a couple of thousand legitimate messages a day -- but thanks to spam, the actual load on the server is much higher. I use Realtime Blackhole Lists (RBL) and Distributed Checksum Clearinghouse (DCC) clients on Postfix and SpamAssassin to reduce the impact of spam."

This howto describes one way to build a scalable, secure, full-featured mail platform. It offers virtual hosting of mailboxes in maildir format with support for quotas and server-side filtering, domain aliasing, address aliasing, address forwarding, catchall addresses. Relaying is secured with STARTTLS and SMTP-AUTH.