An odd omission in the documentation is that searching for Mail Queue Service doesn't find much useful for a new user. There is a screen shot somewhere showing how to add a service but if a user wants to change the interval at which mail is sent from JIRA, they need to know to go to Admin, Services, Mail Queue Service, Edit. Not a big deal, just something missing. The closest I found was the reference on http://www.atlassian.com/software/jira/docs/v3.13/services.html to "Editing Service Properties". Perhaps just adding a sentence there such as:

"For example, to change the interval at which email is sent from JIRA, select the Mail Queue Service and change the interval from the default value of 1 minute"

Matt, if you could raise a ticket in jira.atlassian.com under the JIRA project with a component of 'Documentation' and describe your proposed changes, I'll have a look and make the necessary updates.

Kind Regards,
Andrew