There was no chance that everyone would be running their own email server, but if it wasn't for the lack of IPv6 adaptation a plug and go home email server solution would probably see a decent amount of use. I'd bet we'd already be seeing it as a feature in most mid-ranged home routers by now.
The mail server in a router is easy to host, the problem is:
1) Uptime (though this could be partially alleviated by retries)
and most of all:
2) "Trust"/"Spam score"
It's the main reason to use Sendgrid, AWS, Google, etc. Their "value" is not the email service, it's that their SMTP servers are trusted.
If tomorrow I can just send from localhost instead of going through Google it's fine for me, but in reality, my emails won't arrive due to these filters.
I use a small local provider (posteo) and have 0 problems with spam.
So a 20 pound monkey can also throw around some weight. To be fair I only use it for personal stuff its probably different if you need enterprise scale l.
I've seen plenty of Gmail accounts over the years and they pretty much look the same.
The only Gmail accounts that are "overrun by spam" are those of people subscribing to lots of spammy newsletters and then not knowing how to unsubscribe from them (or figuring they'd stay subscribed in case the next newsletter is the Magical One™). But that's 100% self inflicted and you can't save those people with any technical solution.
Email spam isn't a day to day problem for Gmail (at least) since Bayesian email filtering was first implemented.
The specific concern around uptime & reliability was baked into email systems from almost the start - undeliverable notifications (for the sender) and retries.
But yes, the “trust / spam score” is a legit challenge. If only device manufacturers were held liable for security flaws, but we sadly don’t live in that timeline.
Its not a device/MTA issue, SMTP just is not a secure protocol and there is not much you can do in order to 'secure' human communication. Things like spoofing or social engineering are near impossible to address within SMTP without external systems doing some sort of analysis on the messages or in combination with other protocols like DNS.
SMTP isn't at fault, the social ecosystem is at fault. Every system where identities are cheap has a spam problem. If you think a system has cheap identities and no spam, it probably doesn't have cheap identities — examples are HN or Reddit.
Trust / spam score is the largest one I think, second to consumer ISPs blocking the necessary ports for receiving mail.
Even if your "self hosting" is renting a $5/month VPS, some spam lists (e.g. UCEPROTECT) proactively mark any IP ranges owned by consumer ISPs and VPS hosting as potential spam. I figured paying fastmail $30/yr was worth never having to worry about it.
For "Trust", I believe patio11 described this system as the "Taxi Medallion of Email".
e.g. you spend a lot of money to show that you are a legitimate entity or you pay less money to rent something that shows you are connected to said entity.
Without some kind of federation or centralization, it seems hard to distinguish a hobbyist from a spammer if both of them are using a plug-and-go. Forcing that responsibility into the hands of Google, Zoho, and Microsoft seems like the best compromise, unfortunately.
For one, if my power goes out for an extended period of time I'd still like to be able to access my email. Communications really can't be hosted locally.
