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Banning Email domains works only with new registrations and not existing ones.

You can collect all their IP addresses and try to ban their IP class.

for Example: aaa.bbb.ccc.ddd is made up of 4 octets. To ban a unique IP you can specify aaa.bbb.ccc.ddd.

Not that the class C IP is aaa.bbb.ccc can have 256 various IP's under it. So you can try and ban their class C IP's.

To take this one step further, you can also ban a class B IP (aaa.bbb). This will ban 65536 IP's that fall under that IP class.

Also note that if you do this on a AOL dialup IP class, you will ban any user who is on AOL.

You can ban their user ID, but they can sign up under a new name and new Email.

There is no definitive answer to banning.