It's a push-based protocol. If somebody on your server follows the account, its posts will be on your server, but they can also be there through boosts, which l

It's a push-based protocol. If somebody on your server follows the account, its posts will be on your server, but they can also be there through boosts, which leads to a seemingly random handful being populated. A mechanism to backfill posts would definitely be a good addition. Edit: for clarity, ActivityPub provides an outbox from which another server (or anything else that speaks HTTP) can pull posts. Adding a backfill feature to Mastodon would not require any changes to the protocol.