Debian starts to annoy me like anything that tries to be smarter than me. Gentoo is a nice system sayin: "I'm just a distro, I'm dumb, tell me what you want!", but Debian tries to tell me, what I should do.. pff..
Doesn't matter, Dovecot runs nicely and Postfix now also does what I want it to do. Horde IMP as the web-interface does a pretty good job, too - though I now have to say, that Tiki runs a little smoother out of the box. I wouldn't have believed that first, but it really looks like it.