The company I recently started working for has been using POP'd email from a hosting company for a long time now. The hosting company is your typical setup with numerous servers hosting numerous sites each (with numerous outages and hiccups in service). Our graphic arts guy is currently setting up our own web server, so I need to set up our own email server (so we can finally give the hosting company the boot once and for all). For all the usual reasons, I've opted to stay away from the M$ way of doing things.

Our server is a piece of brand new Dell hardware with a clean install of Debian Sarge. Currently DNS (Bind9 9.2.4) and Samba (3.0.14a) are installed, configured and running smooth (no errors reported in any logs). We have a small office of 30 users with projected growth to 50 within the next couple years, so the server should be able to handle the load of all 3 tasks by itself. I have not setup a linux based email server for years so documentation or assistance are paramount.

I've seen http://qmailrocks.org already, so please don't post that link as your answer. All I want to know is, which email server package would you suggest and why?

Give Zimbra a look http://www.zimbra.com. I didn't try it on a Debian box (CentOS) but it seems there is a Debian installer available. This is one of the better "Exchange Replacements", along with Scalix, that I've come across. There is plenty of documentation on the site, but post here if you have any questions.

Thanks for the lead, andy77. Unfortunately, their Debian installer is still in beta. Other than that, it looks like more than I was expecting. While it would be nice to have a replacement for Exchange, all I really NEED at this point is a functional email server for up to 50 users. If I end up needing more than that (like:
* Shared calendar
* Web document authoring and sharing
* "Over the air" sync to mobile devices
* VoIP integration
* Microsoft Outlook, Apple, and Linux compatibility)
then I'll look into zimbra a bit more. Hopefully their Debian installer will be out of Beta by then. It would be nice if they offered user licenses in groups smaller than 25 (5 or 10 packs would be perfect), but the price is really good for such a full featured package. Definately worth more than what they are asking (and it's still a fraction of the price of M$ Exchange).

Anyone else have a suggestion?

50 users is actually very small beer for a Linux SMTP service, so either Exim (the Debian default) or Postfix (probably the most popular) are both fine. For POP and IMAP use either Dovecot if the users have small mailboxes, or Cyrus for larger mailboxes and shared IMAP folders. Dovecot is simple and secure, whilst Cyrus is sophisticated and scalable.

There are a lot of threads like this on LQ, so you can probably get a bit more by searching around.

How small? I have one user with just under 130MB in his mailbox (that's the largest). Normally I'm used to users having a limit of 500MB, so this seems pretty small to me.

Thanks for the advice. I'll check them out. I just finished going through the qmailrocks.org setup on a test machine and I was unable to get it to work. I think I may still be having a problem with DNS on that machine, but it's going to be the production server when I get the kinks worked out and it passes all the tests. That shouldn't be very long now with all the help I get from you folks.

I was being a bit conservative because of the storage formats that it uses, but looking at the project Web site it claims that Dovecot has been tested with upto 367,000 messages per mailbox (!). The page also notes that Dovecot doesn't support shared folders as such, which may or may not be a dealbreaker. If so then I guess Cyrus is the best option, although it's bit more complex.

I run a co-op "ISP" for 4 different companies. We have beem using Postfix with Cyrus SASL authentication for about 6 years. It's about as reliable as it gets. We are also looking into Scalix for it's Outlook integration and calendaring. I tried Kolab as a test and it was a bit disappointing.