You can configure a workflow automator to check for the domain of the requester email address and choose to delete the tickets which are from the particular domain. Or you can also provide whitelisted domains who can raise tickets in your helpdesk. You can provide this from Admin-->Support Channels-->Support Portal-->Portal Settings. Here, you would have the option to allow ticket creation only from whitelisted domains. So, if you don’t enter the domain from which you don’t want ticket creation it should automatically skip the tickets created by those users.