An individual may have several mailboxes and wish to receive mail at whatever mailbox is convenient for the sender to access. This standard does not provide a means of specifying "any member of" a list of mailboxes.
A set of individuals may wish to receive mail as a single unit (i.e., a distribution list). The <group> construct permits specification of such a list. Recipient mailboxes are specified within the bracketed part (":" - ";"). A copy of the transmitted message is to be sent to each mailbox listed. This standard does not permit recursive specification of groups within groups.
While a list must be named, it is not required that the contents of the list be included. In this case, the <address> serves only as an indication of group distribution and would appear in the form:
Some mail services may provide a group-list distribution facility, accepting a single mailbox reference, expanding it to the full distribution list, and relaying the mail to the list's members. This standard provides no additional syntax for indicating such a service. Using the <group> address alternative, while listing one mailbox in it, can mean either that the mailbox reference will be expanded to a list or that there is a group with one member.