This is a public email service to prevent SPAM in the first place. Keep in mind that we don't allow sending messages to the internet at all as well as we don't support or engage in illegal activities.
Attention, DON'T BLOCK OUR DOMAIN NAMES!
If you have some troubles with user registrations simply ban them by IP address, don't ban our domain names, we're not a throwaway email service and your emails won't bounce!
All abuse reporting can be done via firstname.lastname@example.org