I'm not looking to block senders, I'm looking to block recipients. For instance, I've occasionally hit Reply and written an email to an address of the type
firstname.lastname@example.org, and then wondered why I never got a response, only to see that they require responses through a web form or something.
There are also some addresses who might be CC'ed on a message, but who I would never want to reply to, for instance.
I'd like to make a filter for addresses like this, so that if I try to send to them, it either aborts and moves it to the Drafts folder, or it gets redirected to myself, etc.