A user is assigned more than one directory number. Which option allows one voicemail box to serve both directory numbers?

Alternate Extensions in Cisco Unity Connection let an administrator assign additional directory numbers to a subscriber's account, all of which resolve to the same mailbox. When a caller dials any of the mapped extensions and reaches voicemail, the message is deposited in that one shared inbox, eliminating the need for multiple voicemail accounts.

Notification Devices configure how a subscriber is alerted about new messages (e.g., phone, pager, SMS), not how multiple extensions share one mailbox.

Alternate Names allow the auto-attendant directory to find a user by alternate spellings of their name, not by additional phone numbers.

Message Settings controls playback preferences and message aging policies, not the mapping of directory numbers to a mailbox.

Caller Input defines touch-tone actions available to callers during a greeting, which is unrelated to extension-to-mailbox mapping.

Mailbox refers to the storage container for messages itself and is not a configurable feature for linking multiple extensions.