InformatiQ

I have been using qmail for 6 month now on a server hosting over 30 domains - one of them is an ISP - so i think that now i can say something usefull.
i can't argue about qmail's code or performance, it can take whatever you throw at it and it is being used by google's mail already.
qmail is just 3 parts of a big system, it offers only smtp, pop and delivery agent. you still need imap, mailing list, webmail app and probably a DB backend for storing users. all that can be done easily but with a significant amount of work to get everything to work together nicely.
my take on qmail is the following

1. AFAIK the creator of qmail has technically abandoned it, with no updates to the code sinse 1999
2. qmail is compliant with the RFCs but somethings are just needed for a mail system that the RFC doesn't mention, such as the validrcptto patch and others.
3. Qmail isn't GPLed, which is not a bad thing as long as he allows us to do anything with, but restricting the redistributions making it impossible to package a patched qmail.
4. sinse he is not developing it anymore there are tons of patches out there, and he is not integrating them in his sources requiring you to chose the patch and install which can be hard to make the right choice about which patch is right.

i've been using qmail for 6 month with some major problems but applying the right patches fixed everything.
so my last word about it would be qmail is good but keep attentive. and forget about finding prebuilt packages.