The select Statement

Select statements are the initial condition on whether or not to run a rule. The select statement contains an event expression that must be true before the rule fires. The simplest event expression merely matches an event domain and type. For example:

select when mail received

A rule with the preceding select statement will be selected for an event with the domain mail and the type received. 

Event expressions can express complicated relationships between multiple events. Review the event expression documentation for more examples of select statements.