Hi Philip,

 

If you are using the enterprise edition you can set up throttling on either the domain or for users.  This will limit the number of emails that can be sent per hour.  When you set up throttling there will be an option to either have the messages delayed or rejected.  If you set the action to none then the throttling settings are disabled.

 

You can use the steps in this kb article, Set up Throttling for Domains, to set up throttling on a domain.  If you only have domain access you will want to check with the hosting company to see what throttling actions they may have set up.  You can also set up throttling for your users if you have access as the domain administrator.  Go to Settings > Domain Settings > Advanced Settings > Default User Settings and click on the Throttling tab.  Make the necessary changes there then click on User Propagation and click the Throttling tab there.  Check the boxes for the settings you want propagated to all users then click Propagate Now.

 

Let me know if you have any questions.