We are migrating from a 3rd party IMAP based email system to Zimbra. I'm told that the only way to do it right is to create an outlook pts file from each account and then use the PST importer.

We have bad experience with IMAPSync that some emails may cause the zimbra mailbox to break. We are told that the pst importer does all of the correct input checks to make sure "bad" email won't break the mailbox.

I find it very hard to believe that the only way to migrate 500 mailboxes to Zimbra would involve putting people to manually connect outlook to existing IMAP accounts, create PST files which may be 10GB and sometimes 15GB in size and then import them one by one to Zimbra.

Was i misinformed or is this the only way to migrate to Zimbra?