We have been testing ZCS Open Source Edition v.8 and our experience has been very good.
Now we are moving to the migration stage from SUN JES (POP3/IMAP/LDAP) to ZCS OSE 8, successfully migrating users / password and mailboxes using imapsync.
However, when IMAP/POP3 clients (about 2000) connect to the new mailbox, all mails (600GB) are downloaded (POP3) or synchronized (IMAP) causing severe network problems, and making our migration unviable.
For POP3 clients we found this workaround: Prevent duplicates messages for POP3 users post migration - Zimbra :: Wiki and it seems to work fine and resolve this issue, but what happens with IMAP? I did some test and the workaround apparently helps but I'm not entirely sure.
We are trying to make migration transparent to users, so that they do not even notice the change in the infrastructure.
what are your opinions or suggestions?