@TsRoe @vordenken When I have time, I want to set up my own mail server which uses a milter combined with a web service to treat e-mail aliases as revokable API keys bound to expected senders.
(eg. So an eBay seller who subscribes my eBay address to their newsletter without asking will find it bouncing with "You are not an authorized sender for this e-mail address. Please fill out this CAPTCHA to exempt the current message. Note that abusing this feature may result in blacklisting.")