Anti-Spam and SpamAssassin

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Article Summary

Title:		Anti-Spam and SpamAssassin
Description:		How to best fight spam/junk email using our installation of SpamAssassin.
Key Words:		fight, spam, junk, bayesian, filters, spamassassin, imap, installation, integration
Type:		FAQs
Category:		Email FAQs
Last Updated:		2008-10-24 11:52:25

Anti-Spam and SpamAssassin

What do you do to stop spam?

Our server-side anti-spam configuration consists of three layers:

Sendmail/qmail configuration
Content-based filters (SpamAssassin)

Sendmail/qmail Configuration

We have enabled as many configuration options as possible for Sendmail and qmail mail transport agents (MTAs). The specific configuration used on a server is available in /etc/mail or /etc/qmail.

Content-based filters (SpamAssassin)

SpamAssassin is our content-based email filter of choice. Per account, you may disable SpamAssassin, have it set headers (POP3 mode), or have it set headers and deliver the message to the Junk IMAP folder (IMAP mode). We have even modified our IMAP server to automatically train the SpamAssassin Bayesian filters based on your email activity.

How do I enable SpamAssassin and train its Bayesian filters?

Enable SpamAssassin using either the settings area of our WebMail interface or the Email Inbox Control Panel. Select the "IMAP" level of SpamAssassin integration.
Configure the mail client of your choice to use the IMAP protocol.
If needed, create and/or subscribe to the "Junk" and "Trash" IMAP folders.
If you have the option, configure your mail client to delete messages by moving the messages to the "Trash" folder.
SpamAssassin will automatically deliver messages it considers spam to your "Junk" folder. If any message is incorrectly placed in this folder, move it to your inbox (or any folder other than Trash, Drafts, Sent, and Sent Items) and SpamAssassin will learn that similar messages are ham (not spam).
When junk email arrives in your inbox, move it to the "Junk" folder to train SpamAssassin. Do not move these unwanted messages to any other folder, including "Trash", because the system will see this as an indication that the email is ham (not spam). To properly train SpamAssassin, it is critical that all spam goes directly to the "Junk" folder.
It is important that ham (not spam) be moved out of your inbox to another folder or the "Trash" folder in order for SpamAssassin to learn it as ham. This implies the following:
1. When deleting ham (not spam) messages, please move it to your "Trash" folder. Those who use a mail client without the option to automatically do so on delete will need to move the messages to the "Trash" folder manually.
2. When you need to keep a copy of a ham message, move it to another folder. If you leave it in your inbox SpamAssassin will not know if it is ham or spam.

What are the other advantages of using IMAP instead of POP3?

The files remain on the server. A hardware failure, software problem, or stolen laptop will not result in lost emails.
All messages and folders are backed-up daily. If you accidentally delete some messages or folders they may be retrieved and placed back into your account.
You may concurrently share the account between multiple people, machines, and interfaces. For instance, you may have the same account configured both at work and at home with no conflicts. All your messages and folders will be equally available from both locations. You can even use different client interfaces, like Outlook at work and Thunderbird from home.
Because our WebMail interface also uses the IMAP protocol, all of your messages and folders will be available to you from any browser on any computer.
As described in detail above, our IMAP server has been modified to train the SpamAssassin Bayesian filters with minimal user intervention and no special client software.