Recommendations for Linux (CentOS) Mail Servers

MCode151, thanks for the suggestion.  Would it change your recommendation if I were to tell you that the likelihood of needing to run a second mail server is as close to zero as you can get?  Right now I'm looking for a setup to run my person web site and email, with the possibility of migrating some of my clients later on if it all works out ok.

grblades, what would I use for POP access as well?  Or is that included in one of the packages you've recommended?  And can you recommend a different webmail front end?  I've used Horde before and absolutely despise the interface haha.  Also, is there a package that might allow Outlook MAPI connections, or am I pretty much stuck with one a prepackaged solution like Scalix or Zimbra for that?

Cyrus will provide POP3 support aswell.
Squirrelmail is a very popular web front end but it is email only. It does have various plugins for address books and managing server side filters and spam settings but it wont do calendaring etc...

If you want Outlook integration you will need to look at one of the prepackaged solutions you mentioned. However you might want to look at using Thunderbird instead. It uses open standards so links with hoarde etc... much better and is far faster than Outlook when dealing with large mailboxes.

Forgot to mention there is no reason that you cannot use Squirrelmail and horde at the same time.

There is http://roundcube.net instead of Horde

From the list above (till I remember some other names) so far I'd go:
Zimbra
Scalix
Zafara < ActiveSync with their spinoff (though the z-push download is unavailable at-the-moment it's a SourceForge project that I expect will be back up in the future)
grblades mix-n-match

So yes, I still prefer Zimbra; their Zimlet mash-up potential is amazing http://www.zimbra.com/products/zimlets.html (and they have quite a collection of ones to try out in their gallery - or when installed, on your server at /opt/zimbra/zimlets-extra)

Actually you can do activesync in the Zimbra open source version using Z-push
http://wiki.zimbra.com/index.php?title=Open_Source_Mobile_Push_Mail
And the Funambol connector for push contacts/cal is http://zimbrafunambol.wiki.sourceforge.net

The only tricky part of mail server setup for the less experienced admin is understanding that you often need a split dns (if your behind a NAT, such that internal lookups return the local IP and outside lookups return public ip) if it's a direct public IP then don't worry about it.

---

I've setup ZCS servers on CentOS5 (using their RHEL5 32-bit or 64-bit binary) in 15 min, 1-2GB ram, you have few users so doesn't matter, but large users avoid Raid5, use Raid 10 instead.  If you get MX errors in the setup script simply adjust the default domain to domain.com instead of server.domain.com or add the relevant domains later. (Most admins are used to the default domain on mailserver boxes being like root@server.domain.com, to not conflict with what you have going on currently; they do to of course but their setup script does a mx check for it, and most new admins don't bother creating one for the server record, they do it on the domain record instead.)

Their site docs are good http://www.zimbra.com/community/documentation.html but here's another walkthrough: http://www.howtoforge.com/zimbra-collaboration-suite-open-source-edition-on-centos

service sendmail stop
chkconfig sendmail off
A properly configured /etc/hosts file:
127.0.0.1 localhost.localdomain localhost
x.x.x.x server.domain.com server
& /etc/sysconfig/network:
HOSTNAME=server.domain.com
Grab their binary, ./install.sh and your on your way.
Literally all you need from the default CentOS is a few packages you can get via yum (their installer will check/list dependencies).

Any questions just visit http://www.zimbra.com/forums and someone will help you out - I've had same day responses.

Good stuff guys, thanks.  One last question.  grblades, you mentioned using Thunderbrid instead of Outlook.  I'm using Thunderbird for some of my mail via IMAP, but it doesn't do the calendar and contacts sync.  Is this something that is built in with Thunderbird, or do I need extensions?  Can you point me to a tutorial that would explain this setup?  Thanks again.

Sorry I dont have any comprehensive links at the moment. Thats the next step for me to lookup the details of for the new server I will be setting up in a couple of months. I am currently upgrading NT4 domain controllers to SBS server and installing a new Linux file server.

What I have found out so far is that there is a Kolab plugin for Thunderbird and one for horde. Kolab appears to be the calendering server which horde talks to.
There seem to be a commercial outlook plugin for it and also an open source thunderbird sync tool (but limited functionality at the moment).
The calendar plugin for Thunderbird is called Lightning but you need another plugin to sync it. There are quite a few to sync to gmail and various phones.

Zimbra looks good but for me the all in one solution may cause problems as we have about 20GB of mail to be moved over from a cyrus system. Moving to another cyrus is easy but if I need to move it to something else then I may need to use an imap sync tool which will take a lot longer.

Having a horde front end with kolab and cyrus as the back end system would be easier moving the mail across. Thunderbird works so much better with large mailboxes I would like to get people using it instead of outlook 2003 even if we cant get all of the functionality in the client.

For me AV is not an issue as we use a front end server for virus and spam filtering. If I were able to use postfix (or technically exim or sendmail and MailScanner is compatible with those - I just use postfix) however I could move it all onto the same server which would be a benefit.

thanks guys, very helpful