Zimbra Collaboration Suite (ZCS) is a nice software about collaboration, mainly in mail server service. Zimbra contains Postfix for mail server service, ClamAV for Anti virus Scanner, SpamAssasin, LDAP service and provided both mail client and web mail service.
Zimbra combined 2 licensing style, commercial and open source edition. I used the open source edition and deployed Zimbra into OpenSUSE 10.2 server in my office. The Zimbra Installation Guide for OpenSUE 10.2 can be found here. The installation and configuration running smoothly without big problem. I got an error message while resolving MX records for my DNS server, so I changed DNS configuration to fit with Zimbra requirement.
I loved zimbra webmail feature and Zimbra web admin interface.
Zimbra has a great forum and Wiki support. Everytime I got an error or need an information about Zimbra, I got a perfect answer at their wiki or forum.
If you have a long experience with one of 3 popular mail server in Linux (Postfix, Sendmail and Qmail), You should be fall in love with Zimbra. We still can be used shell terminal to administer Zimbra mail server but Zimbra provided an easy way to do administrative job with Zimbra web admin configuration.
If you need best linux mail server solution without commercial fee, Zimbra should be the best choice. Try it !