Alternately, refuse all mail from perlmonks

It is what I would like to do, but by means of SPF. That way, legitimate mail is not blocked. Without SPF, I would now add perlmonks.org to the blacklist, and would then probably forget about it. If perlmonks.org then would start providing email services for monks, I'd have a problem. SPF moves the administration from the receiving to the supposedly sending end; so only one person has to update the information when it changes, instead of system administrators of all systems that have it blocked.