To delete a mailbox:
Click the Mailbox Administration heading.
The Mailbox List page appears.
Click the Delete link for a mailbox to delete the mailbox and its contents.
You cannot delete a mailbox if it is:
currently in use
a Mailbox node of a CCR Tree
a target in the CLID table
the skillset mailbox of an enabled skillset. You must disable the skillset before you can change or delete its mailbox.
the System Administrator or the General Delivery Mailbox