[zimpenfish]

AFAIUI yes, you will probably get 3000 messages sent because each follower has their own inbox. There is a potential for batching though - "a server MAY reduce the number of receiving actors delivered to by identifying all followers which share the same sharedInbox who would otherwise be individual recipients and instead deliver objects to said sharedInbox" - if a bunch of the 3000 followers have the same sharedInbox (which presumably the receiving server has somehow magicked up?[1]), then your server can do a bulk delivery to that for those followers.

[1] I guess you might make them for specific celebrities if your server has a high density of followers? grepping the Pleroma source doesn't seem to throw up any obvious "automatically make them" logic.

[nightpool]

Generally, all followers on a single server share the same sharedInbox. To a first approximation, that's what "server" means on ActivityPub—sharing a "batch" inbox you can deliver to.

[zimpenfish]

> Generally, all followers on a single server share the same sharedInbox.

You mean that all followers of Celebrity X on instance Y will have a sharedInbox because they're a follower of Celebrity X? Apologies, I've only lightly read the spec and haven't really seen anything like this in there.

[nightpool]

No, sorry, what I mean is that all users on mastodon.social have a unique private inbox and then a "sharedInbox" value of "https://mastodon.social/inbox". Almost all deliveries (with appropriate "to" and "cc" targeting values that the receiving server can appropriately deliver to, i.e. individual actors or the special "followers" group for an actors) can be sent to the sharedInbox in bulk, but for private groups and some other special cases you may want to use direct delivery.