We're trying to migrate from groupwise to zimbra. During our test migration, the groupwise migration tool hangs when using more than one thread. This also happens when using one thread on more than one migration client (multiple PCs). It happens sooner when using more threads, so it looks like it has something to do with the number of connections.
Our install is zimbra on Redhat 5, two server setup, auth to AD.
I also tried putting a reverse proxy between the migration PCs and the zimbra mailbox server, as I was seeing a lot of sockets in CLOSE_WAIT on the windows XP PCs.
This is a real pain. If we have to migrate one mailbox at a time, our migration window will grow beyond our maximum of 48 hours (one weekend).