Symptom: You’re trying to change your Exchange UM prompts via the phone, hitting #* and your extension, yet despite having all the right privledges, you hear the message “<ext> is not a valid mailbox extension. Please enter your extension.”.
I recently ran into this again, and I’ve blogged about it a bit before, but didn’t realize at the time it also affected Lync and Skype for Business as well so I’m going to explain a bit more clearly how to mitigate.
The first items you’ll want to check are the obvious prerequisites. Your Exchange UM dial plan must have TUIPromptEditingEnabled set to true. Of course, if you hear the message described, it must be.
The second is to confirm you’re actually allowed to edit the prompts. You should be a member of the “UM Management” role. Even if you’re a member of the Organization Management RBAC group, you’ll want to be in UM Management as well.
But, even if that’s all set, you may still be hearing the “<ext> is not a valid mailbox extension. Please enter your extension.”. error. If you read my previous blog, you’ll understand the issue a bit better, but for the workaround you’ll want a mailbox in the same database as the system database. You can either move the users who need to edit to this database, or as some of my clients prefer, you can create dummy “editing” mailboxes for this purpose.
To find the correct mailbox database to move the editing accounts into, from the Exchange Management Shell run “get-mailbox -arbitration | fl identity, database”. Look for the system mailbox with the id “bb558c35-97f1-4cb9-8ff7-d53741dc928c”. In our example, we can see that it exists in the DB4 database.
Now, simply move the mailboxes you’d like to edit the prompts with to the same database and quickly you should be able to edit the prompts via TUI again.