What must the administrator do to resolve this issue?

An end user is complaining that when they try to retrieve their voicemail messages, they hear the message "mailbox is currently in use."

What must the administrator do to resolve this issue?
A . The administrator must reload the mailbox for the user.
B . The administrator must verify that the mailbox is enabled.
C . The administrator must verify that the primary extension that is associated with the end user is in an
D . 164 format.
E . The administrator must unlock the mailbox for the user.

Answer: D