"The request failed. The underlying connection was closed: An unexpected error occurred on a send" issue during the Exchange server mailbox migration

Question

Hi,

We are performing a mailbox migration from Exchange Server 2016 (hosted on Windows Server 2016) to M365 using BitTitan.

As per BitTitan's requirements, we have made the following configurations:

• Assigned the ApplicationImpersonation role to the admin account.
• Granted full mailbox permissions to the admin account.
• Disabled the Throttling Policy for the admin user.

Despite these configurations, we are encountering the following error during credential verification:

"The request failed. The underlying connection was closed: An unexpected error occurred on a send. ---> The underlying connection was closed: An unexpected error occurred on a send. ---> Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> An existing connection was forcibly closed by the remote host."

Any suggestions or recommendations to resolve this issue would be greatly appreciated.

Thank you