set status_mail [<text>]
This variable sets the string displayed in the status bar when email is present in the user's mailbox. The mail does not necessarily need to be new. If the user's mailbox is empty, nothing is displayed.
This string is represented as %M in the STATUS_FORMAT string. Within STATUS_MAIL, the expando will expand to the number of messages in the mailbox.
Customizing the string displayed when the mailbox contains messages:
/set status_mail Mail: %M