I’ve been using MessageOps Exchange Migrator for a while now and while it is an amzing product, it isn’t without its quirks. Here are some I came across whilst migrating a small org (80 users) to Office365

  1. Make sure that the account you’re migrating isn’t disabled. If it is disabled, it doesn’t show up in the source mailbox list.
  2. Ensure the mailbox isn’t hidden from the GAL. If it is, the migration will fail with a MAIL_E_NAMEN error and then WSAECONNRESET.
  3. Ensure you have proper rights on the mailbox you are migrating from.
  4. Ensure the mailbox you are migrating to has an Exchange license assigned. This can be E1, E2, E3, whatever.
  5. If you change change any permissions or disable/enable accounts, hit back in the tool and let it rescan everything. This saves you restarting the app and having to type all your credentials again.