This error indicates that we were unable to authenticate the Source or Destination mailbox and retrieve a list of folders when given 15 minutes to complete these operations. This may be because the Source or Destination is unusually slow, has a very large number of folders, or has been "hanging" networking calls.
We expect all mailboxes to be able to return a list of folders within 15 minutes, after which the migration is aborted. This is done to prevent DOS (Denial Of Service) attacks on our systems.
We recommend the following:
- Resubmit the mailbox for migration to see if this error persists.
- Check to see if the error indicates whether it pertains to the Source or Destination.
- Check to see if the Source mailbox has a very large number of folders (more than 1000).
- Check to see if both endpoints respond by logging in to the Source and Destination mailboxes.
- Decrease the number of simultaneous migrations.
If you are performing a document migration, see Cannot retrieve folders from "folder" for steps to increase the duration of the timeout.