I'm going to setup an email server with stuff like qmail, spamassassin... and I have two choices of the system to use: CentOS and Debian. So can you all give me some advices of which one to choose, based on their features? Comparision needed, maybe.

Thank you all!

It might be better to yourself to make a list of features that you need, no one really knows your requirements better than yourself. Then to look at the various different bits of software that provides that for you and based on how well they are supported, how easy they are to install, how easy they are to use, how well they are maintained etc. make an informed decision about what you will use.

Your list of features might include stuff like:
- IMAP/IMAPS support
- POP3/POP3S support
- webmail
- graphical interface for adding users/configuration
- spam filtering
- antivirus
- etc.

You'll probably find that the question of "CentOS or Debian" isn't that important after all, both distos has been around for ages and you should be able to find installation and support for the disto and any software you intend to use on them fairly easy. Sometimes it is just a matter of preference that makes the decision for you. It's always a good idea to try out more than one option to give yourself a better idea of what you want.

If you decide to go with qmail, have a look at www.qmailrocks.org for a great guide on a complete setup of qmail with spamassassin, clamav and even some extra goodies like webmail, web configuration and such. When I first started setting up mailservers (thinking back to that I feel quite old now) that website helped me to get things going nicely on Slackware. It has a guide for Debian and RedHat too (CentOS prettymuch = RedHat) so that fits your current two choices.

Enjoy

actually I once experienced with Qmailrocks on RHEL (which is now no longer open source). So I decided to change to another one. And Debian & CentOS are of my choice. It seems that if I want to experience smt fresh I should try Debian (as CentOS is quite the same as RHEL right?)

Qmailrocks does rock, yet some of its components are not really up-to-date, can I replace them with newer one?

Hmm, Debian is released more recently, and, uh, has more software package... do you think that's something overwhelming CentOS

I have been testing with both Debian and Centos. They are both good choices and I think that there are no major differences. They are free and well supported. Security patches are quite fast implemented.
I suggest that you read about there philosophy from their websites and then choose one and most important, stick with it!
I've been using instructions from http://www.howtoforge.com
This site is giving good instructions and furthermore you can use a very good control panel called ISPConfig...

good luck,

jysse

Built qmailrocks on BSD, ran great.

Found Zimbra as a Yahoo project. Tested and liked it a lot. Used Centos 5 as the OS. The install will complain but also will work. http://www.zimbra.com/community/downloads.html

Debian is not an option; Centos really isn't either.

Pick the one you are more comfortable working with. That being said, were I selecting for someone with a similar background to myself, I would suggest Debian, I run several mail servers off of both. Currently Debian stable is quite a bit more up to date than CentOS (although that won't be true a year down the road.) Additionally, I like the default setup of the mail programs on Debian better than I do of that on CentOS although except for Exim it's not significantly different.

That being said, the difference between the distributions is far smaller than the differences between what agents you select for them.

You're going to see a bigger difference based on your choice between Postfix, Sendmail, Exim, or QMail (Which I highly recommend against) than you are going to see between CentOS/Debian especially when it comes to functionality. You'll see bigger differences in features choosing different pop3/imap daemons than you will distribution.

Pick what you're comfortable in.