Synchronous triggers must complete before further operations can continue. They are typically run when the event is initiated but before it finishes. The event completion is dependent on their success. Triggers are run synchronously by default.
Asynchronous triggers run in the background, independent of other operations that follow. They are typically run after an event completes. To run an asynchronous trigger, the async: prefix must be used.
Here is an example where a Perl email assignment trigger is declared:
async:perl crAssignEmail.pl