http://www.rfc-editor.org/rfc/rfc4146.txt
RFC 4146: Simple New Mail Notification, R. Gellens2005-08-01T23:00:00-00:00In brief, the server sends the string "nm_notifyuser" CRLF to the finger port on the IP address (either configured or last used) of the user who has received new mail. This memo provides information for the Internet community.