You already have implemented a hard block sender list... but;
Would be nice to implement a hard block *recipient* list so that the mail archiver log would be more clean for non existent e-mail addresses or unwanted or terminated mail addresses.
Another solution would be to block sender (to:) addresses from the mail archiver self.
Please try this way
it's possible to blacklist a recipient, but the only way to do it is this:
Go to the advanced white/blacklisting page https://<protector>/spprotector/spamstatistics.php?query=lists
and add a new entry like this picture, and then restart the Anti Spam engine on the home page.
When you want to white/blacklist a sender it's different, because you can leave the to: field empty, so this made me think it was not possible to do the same for recipients. But forcing the text "default" it works.