Well it's still decentralized and scales in that there is significant competition participating in an open protocol. Even though most use the big 3, many smalle

Well it's still decentralized and scales in that there is significant competition participating in an open protocol. Even though most use the big 3, many smaller players have enough legitimacy to be whitelisted by gmail, e.g. fastmail and protonmail. But for fully custom, sure gmail is annoyingly aggressive these days, but it's not a black hole, the emails still send and more importantly receive. Does anyone other than spammers send cold email? I usually am receiving or replying. When I do send cold, it's to someone who is expecting it so they will check their spam or already have me in their contact list so it doesn't go to spam. It's not for everyone or for all situations, but fwiw I've found it very useful to exercise the fully distributed nature of email for personal and professional reasons, so I would still defend it as a fair example of a distributed protocol that scales :).