I just wanted to pass along how Zimbra saved my bacon.
Our old mail server took a dump last week. It was an old hsphere/cpanel managed mail server and the only thing we got off of it was a userlist/domain/password list.
Fortunately I'd already stood up a Zimbra server to eventually replace it, and it was ready to go. Once we determined that the old mail server wasnt coming back I worked to get the existing users recreated on the Zimbra server. After doing some work with zmprov and using Excel to create formated input text files, I was able to get all of the user data recreated into Zimbra. I changed the IP address of the Zimbra server to be the same IP as the crashed mail server and then mail started flowing again!
It took alot of work, but I was very happy to be able to migrate 500+ users, and 87 domains in emergancy mode in the space of 6-8 hours.
Now the users have a WAY better interface, spam filtering, antivirus, tons of new features... And I've got a tremendously better administration interface.