EM-3107
This mailbox is not available in Microsoft 365
Why it happens
There is no Exchange Online mailbox at this address, or it is not enabled (an account without a mail licence, or an on-premises mailbox not moved to the cloud).
What to do
Check the address and that the mailbox exists in Exchange Online (for a shared mailbox: in the Exchange admin center), then connect again.
- HTTP status
- 422
- Retrying does not help