Reason was, SPAM (UCE) was getting to annoying and my filter-setup with exim wasn't able to effectively block such spam-connections.
If you came here experiencing problems sending mail to gecius.de, then take a look at this page to see why and how to leave a message anyway.
Postfix is very good in enforcing sane smtp-connections to keep a lot of spammers at bay. Unfortunately, this also means that a lot of boxen which use their own mail-software to sent out mail might get caught in the middle - by not setting a correct hostname in their mailer setup. Do this! Set it up correctly. Spam is getting worse and worse and more and more people are likely to setup similar things.
The replacement of exim with postfix was pretty straight forward. I had to tweak a couple thinks (nothing major, though) to get it to forward everything to my internal mail-server, but that was easy to setup.
Anyway. Additionally to ensure correct sender/receiver information during the smtp-session, I do body and header checks against the following information (but be aware: this changes frequently) for body checks:
And the following in regard of headers. Be aware of the first regexpression! The default installation on my debian was like this: "/[%!@].*@/" This does not work with mailing lists and other mails which have multiple references in their headers! Make sure there's an additional character checked: [ |>|<] in the second regexp (which must not match to get the mail).
More to come.