Mailbox properties

Mailbox properties are shown here:

Mailbox Name The name that displays to recipients of an ad hoc email This can be the same as the mailbox address.
Mailbox Address The full address of the mailbox to which employees send an email.
Default If establishing more than one mailbox, it is important to set one as the default. The default mailbox pre-populates the Email From and Reply To fields when an ad hoc email is sent.