Mail aliases must be unique within the domain. This section provides the procedures for administering mail alias files.
In addition, you can create database files for the local mail host by using makemap. Refer to the makemap(1M) man page. The use of these database files does not provide all of the advantages of using a name service such as NIS. However, you should be able to retrieve the data from these local database files faster because no network lookups are involved. For more information, refer to Interactions of sendmail With Name Services and Mail Alias Files in Chapter 3, Mail Services (Reference).