ErrorTimeoutExpired: This error is returned by Exchange Web Services (EWS) which reported that the operation timed out. This may be for different reasons such as EWS receiving a timeout from local Active Directory, from the mailbox store infrastructure, etc. Often, this error will occur when the target environment in under high load, or when processing large items as this increases the change of a timeout.
We recommend the following:
- Resubmit the mailbox for migration to see if this error persists.
- Check if the error indicates whether it pertains to the Source or the Destination.
- Check if both endpoints respond by logging in to the Source and Destination mailboxes.
- Decrease the number of simultaneous migrations.
- Log the subject of failed items.
- Retry failed items (subjects will be logged).
- Review error logs to identify the offending items.
- Check the sizes of failed items.