"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

Answer 1

Hello,

Thank you for posting in Q&A forum.

Based on the error message you provided, TLS 1.2 may not be enabled at the computer level. I suggest you try the following operations to see if this can solve the problem:

1. Press Win+R shortcut keys to open the Run window, type inetcpl.cpl and confirm to open the Internet Properties window.
2. Under the Advanced tab, find Use TLS 1.2, select the checkbox and click Apply.

I hope the information above is helpful.

Best regards

Zunhui

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