I’ve been thinking of self hosting a mastodon (gotosocial, more specifically) + a matrix server on an old computer I have, but sometimes I might need to turn it off for 2 days or more (not to mention some energy or internet outages that might happen here)
I suppose with the mastodon part the server will properly sync and download whatever’s been missing, but I’m not entirely sure that’ll be the case with matrix. If anyone sent me a DM on there while my server was down, would it get through after it was back up?
Matrix won’t necessarily download all state/messages automatically, but if your client requests a non-available message your matrix server will query other matrix servers for it (backfilling).
E.g. if you scroll up to older messages, it might take a a few seconds but your client should eventually show them.
Matrix server use a back-off for servers sending messages, so if your server is offline for many hours, it might take a day for your servers to get messages pushed to by other servers again.