I performed a pre-stage migration on 18 mailboxes, almost all finished overnight and the course of a day, one remaining one took from Wednesday night 1/31 and appears to have finally finished early morning, Feb 4th. It had a number of issues, all stemming from "Invalid binary MIME data detected." it was 5 times the size of the next largest mailbox, and had double the number of items. Is there anything in logs that you have access to that would explain the disparity in how long it took to migrate all the other mailboxes in contrast to how long it took the last one?
The one in question is [redacted by forum moderator: Rob Latino] source, [redacted by forum moderator: Rob Latino] destination