Fight against spam
Finally I managed to bring my server up to dat regarding spam and antivirus facilities.
Most I did was to reconfigure amavisd-new (which I'm using with Postfix), replace the outdated OpenAntivirus with ClamAV and install the newest version of Spamassassin. Beside that I installed Razor2 and integrated it into Spamassassin. As Spamassassin weights Razor2 hits usually only with abou 1 point, I raised that setting to 2.5. Today every of the (non-mailinglist) spam I got was filtered perfectly and I got no false positives.
I hope that lasts for the upcoming times to avoid most of the fu**ing spam. The new virus scanner is updated frequently, so my Windoze using friends using that mail server are secured from ugly virii.
I plan to migrate my Postfix and Spamassassin settings to MySQL in future. So specialized settings for both can be stored individually for each mailaccount. Especially black and white lists. SquirrelMail (my webmail system) should support that quite nicely.
The only spam issue I did not fix yet is spam along mailinglists. The PEAR webmaster and CVS lists produce spam every day. Through the list system, most headers get fixed and through auto-white-listing of Spamassassin those mails get a positive addition in scoring. If anyone has an (implementable and usable) solution on that, feel free to comment!