Limit End Users to my domain

I recently downloaded the 30 day trial, so just trying to figure Plumsail out. Is there a way to limit end users to users on my domain? I basically don't want anyone without @mydomain to be able to create a ticket. Is this possible? If so, how?

Hello Mandi! I suppose that you receive messages to your own mailbox and then forward them to HelpDesk as described in this article. In this case, you can set a rule in the former. For example, in Outlook it would look like this:

Please note that the default forwarding should be disabled in the case of using the rule.