Enabled TLS 1.2 over 2 months ago and have setup many users since then, but now we cannot enable UM for a user. I only mention TLS because that is what forums say is the cause.
Here is the error
Unified Messaging can't validate or generate a UM PIN for mailbox 'email@example.com' : An error occurred while accessing the user's mailbox. Details: The underlying connection was closed: An unexpected error occurred on a send.