A system that enables a communications system user to conveniently define
entities to be excluded from receiving an electronic communication, such
as an electronic mail ("email") message. An "Exclude" user entry field is
provided in a user interface to a communication system. The Exclude field
accepts entry of an "exclude set" of entities to be excluded from an
email message being processed or defined in a currently accessible
graphical user interface window. The disclosed Exclude field is provided
in a user interface window together with one or more other user entry
fields available for definition and/or review of an "include set" of
entities initially designated for receipt of the message. Lists and/or
groups may be resolved by determining the destinations they contain
either within the client computer system, within a source server computer
system, and/or within a destination server computer system.