You can blacklist from a tell the same way. What they are doing is spamming out tells and immediately logging out so you cannot blacklist them. We need to be allowed to blacklist an account. And when an account gets permanent banned, they are auto-removed from our blacklist. I hit the 200 limit twice, cleared it out, and now back up to almost 100'again.

Also, blacklisting by itself does nothing. Need to also report them for cheating.