Blocking an unwanted address

[rdthrash @ nps . navy . mil (Roger D. Thrasher)]

Does anyone know of a way to block a single address from subscribing to a
list? There is someone who has been barred from our list for personal
attacks and I want to make sure he stays off. But the problem is that we
also want to maintain an open subscription policy (no desire to shut the
gates just because of one individual). Anyone encounter this problem
before? Thanks.


Roger