TimeoutErrorTransientException Error When Migrating Mailbox

Test AutoDiscover

Test-MigrationServerAvailability -ExchangeRemoteMove -Autodiscover -EmailAddress "[email protected]" -Credentials $(Get-Credential domain\admin)

If AutoDiscover fails, run this:

Test-MigrationServerAvailability -ExchangeRemoteMove -RemoteServer "mail.domain.com" -Credentials $(Get-Credential domain\admin)

Resolution

If both AutoDiscover steps fail, check the Firewall as it is most likely that there is a misconfiguration there, such as inbound firewall rules not allowing inbound traffic, or a NAT rule not being setup correctly.

If AutoDiscover steps succeed, but the migration still fails, you may need to review your On-premises Exchange Server, or raise a case with Microsoft Support.