I've done a migration from an old Zimbra 7.2 to 8.8. I've installed legacy ZeXtras, made a backup and imported it on the new server.

We've had minor problems with missing grants or renamed folders (UnknownFolder_ID), but we managed to fix them quickly. Now some users found out they have missing emails. Unfortunately this is a bigger issue.

After a little bit of digging I found those missing items were not saved in the backup. I've searched for the message id in the backup folder (accounts/zimbraId/items) and couldn't find it...

The new server is now live and I cannot do another import, but I still have the old one online. So I was wondering what's the best approach to move those missing mails from the old to the new server.

I suppose doing a new smartScan and importing them is not a solution.

I thought doing an export form the old mailbox to the new and could work for what has been noticed, but this way I cannot be sure all the missing elements are migrated.

The only option I'm thinking about is using imapsync, which should also be able to avoid duplicates.

Any other idea?
Thanks!