npub13y6awm3sgrmqttqgua5m0484aqsykngs47lugdm9jqd4y0a47upq9vdylg (npub13y6…dylg) At some point many people did run their own SMTP servers :) Luckily nowadays that's not common, because people realised it's hard and requires a lot of work.
I hope the same centralisation will happen in the #fediverse also (isn't that an oxymoron?).