As of January we have rolled the 1 year clock on being on Zimbra v7 running on a virtualized RedHat 5 VM atop our VMWare cluster, so far so good. Zimbra VM has 2 vCPUs, 8GB memory and 120GB of space between 2 hard disks (32GB for OS, 80GB for /opt directory for Zimbra)

Previously we were an Exchange 2003 environment, setup a split domain so we could do a gradual migration, used Exmerge to export user mailbox data from Exchange and then used the Zimbra PST Import utility to bring the data into Zimbra, flawless process really. From previous experience, we did not use the Exchange migration utility as I had previous issues with corrupt/missing data at a previous employer. Used the BOTH GAL sync option until all users were migrated. We also introduced a shared mailbox approach for certain departments which decreased our user count from 168 in Exchange down to around 75 users which saved money on the migration.

So far our installation has been rock solid, no major production issues, most of our support engagements have been bug/RFE related, 6 or so of our RFE's have been resolved in the past year and more have been fixed in v8 which we are in the planning process for upgrade. We are very interested in the Zimbra Appliance as a way to further simplify our deployment and centralize our support instead of having RedHat OS support and Zimbra application support, we could move to a Zimbra support model for the entire stack.