It’s not that different from how e-mail lists work.

Lemmy hasn't even reached 1990's level email system design for a database-backend MTA. The outbound delivery queue has no management tools, is not saved when a sever stops, and runs in-process with the same service as the rest of lemmy_server - for interactive end-users. Federation really needs to be moved to a separate server service, the massive number of connections to send votes and comments isn't even holding up under current loads. And this is without major social events with dozens of comments per second, people leaving Reddit was largely limited by signup problems - major servers crashing and restricted signup approvals.