don't use a general email address for support. use an online support tool that can only be accessed by people who have a license. possibly use a tool to verify

don't use a general email address for support. use an online support tool that can only be accessed by people who have a license. possibly use a tool to verify the license before they can even contact you. everyone else can post issues on github. also, do you track names and email addresses of those who bought a license? then you can match up requests and reduce the amount of license verification that you need to do.