It would be nice to send "mail" to a player or segment.
Upon login, a player's client could GetMail() to load their mail as a list of Mail Messages.
Mail could be used for player-to-player mail, in an MMO especially.
Mail could also be used for sending a message from an admin, like "Your account was muted because such and such."
Finally, it could also be used for sending out announcements to particular segments, such as "Thank you for participating in the event!" etc.