From Elendor
Elendor's mailgroup system offers a convenient way to mail groups of people
and provides administrators a way to receive mail as a group. Mail group
names can be placed in message addresses just like regular player names.
The only +mail command which deals exclusively with mailgroups is the
+MGROUP command. It allows players to list all mailgroups and who is on
them and allows administrators to create and destroy mailgroups. See HELP
+mgroup for a complete description of the command.