[quote]Try “Creating a new email address” and see if the mailbox appears in the
dropdown for the “deliver to this mailbox” section.
It sometimes does, sometimes doesn’t.
[quote]If so, assign a bogus address to this mailbox and then after confirming
that operation has completed, the mailbox should appear in the addresses
list where you can delete it.
[quote]Otherwise contact support of course, since there doesn’t appear to be
any other way to resolve stray mailboxes.
I fear you are correct.