I'm in the process of migrating from Zimbra to Exchange Online and I need to migrate the contents of 190 users' mailboxes via IMAP.

I need either a superuser account that I can use to access all of the mailboxes and their folders or I need to use 'virtual shared folders' via IMAP. I cannot find details of either.

I have tried following the UserRoot attribute method in the following link but to no avail - Exchange cannot see the directory:

Prepare a CSV File to Migrate E-mail from an IMAP Server

Any help would be great - I know I'm off to 'the dark side' but that's corporate politics for you!

Kind regards,