Ya I keep forgetting it's similar to email. But at the same time for every reply, is it not similar to doing a reply-all, with each federated instance being in the recipients list? And don't forget what happens when everyone starts doing a reply-all when on an email with a large distribution list... The email server ends up taking hours or even days to processes that queue. Hopefully I'm over thinking it, but I'll learn more over the next few weeks as I study ActivityPub more and more.

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.