During a recent migration, I had about 10% of the mailboxes fail to migrate. All the contact, calendars and tasks would migrate, but none of the email.
This was driving me crazy. I could start the migration, sit and watch the mail move over via the imapretrieval folder, only to have that folder suddenly get deleted and the migration be "done".
Nothing in the logs, just done.
After much testing, found out that these particular users had folders in there email that used Windows reserved names. For example - one of the folders was called PRN, which Windows reserves for Printers. Thus, as soon as the migration wizard hit that folder, it would abort.
I would be nice if the Migration wizard could check for those sorts of things and give a heads up prior to the migration, or at least continue past and give a report at the end.
Many wasted hours hunting these down and then having to manually migrate the remainder of the mailboxes.