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.

"(draft for an upcoming book called Wicked Cool Emacs)

Ah, spam, the bane of our Internet lives. There is no completely reliable way to automatically filter spam. Spam messages that slip through the filters and perfectly legitimate messages that get labelled spam are all part of the occupational hazards of using the Internet..."

I have totally gone off the deep end…Spam has made me so mad I have gone on a personal goal to cut the Spam on my servers to 0%…realistic, probably not. Die trying…yep that’s me.

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?

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.

If you are running a webserver you might have faced the problem already: somewhere on your server is a vulnerable contact form or CMS system written in PHP that gets abused by spammers to send emails trough your server. If you have more than a few websites, it is a pain to detect which of the sites is vulnerable and sends the spam emails.

This Postfix tutorial explains the vacation message option of Postfixadmin which allows you to conveniently send an automatic reply when you're not available. This installation is for Ubuntu 9.10 but should work for just about any Linux distro.

One of the best methods of restricting SPAM is to require address verification. This means that Postfix will initiate a SMTP session with the client’s server to verify that it is a legitimate address. This takes time and resources but…it a very effective way to deal with SPAM. You will need to add the reject_unverified_sender option.