To add a cluster:
The Cluster Name must consist of letters (upper or lowercase), numerals, dashes (“-”), underscores (“_”), or periods (“.”) only. It may not include embedded blanks. Often, a cluster will be associated with a root email domain; therefore, using the email domain as a cluster name is convenient.
The Cluster Name column displays the names of the clusters you have defined.
Practice this procedure in Practice—Adding Clusters.