I'm not self hosting, so I'm depending on what the server admin enables, and the policies they establish.
That said, the server fully supports xep-0313, which perhaps among other things control messages being kept on the server precisely for the purpose of sending them to all registered devices, thus allowing the sync.
But perhaps there's a policy in place removing the messages from the server as soon as some device has gotten it, leaving only online devices with the ability to grab them. I don't know if that's possible...
I experimented getting a device offline for a couple of minutes, and then exchanged messages with another account, and also to my same account. Then eventually I got the device offline, and none of the messages, not even the ones sent to myself, were ever synced on the device just coming online...
This is really sad, since that's precisely one of the benefits of having servers over peer to peer solutions, it's easier to sync devices through the server.
Might this be some sort of policy to keep disk usage on the server low?
I might need to explore some other server if that's the case...
Thanks !
Edit: Communicated with the admin, and they mentioned this was unexpected.
Dino neither Conversations offer anything about archiving preferences.
Not sure about Dino, but in Conversations it should be in your account details, top right three dot menu, then archive settings as always.
archiving preferences -> Server-side archiving preferences?
And on the dino side, on preferences there's almost nothing to configure, and on acocunts, I see nothing that can be configured. I can only add/remove accounts...
"Always" is the good choice yes, and dino is gnome-philosophy-compliant: "do not expose too many settings".
Some additional info: your server admin may have set the server-side archiving policy to a very short time or even disabled it all together. Also, this Conversations setting only applies to direct chats. For groups it's up to the group owner to enable or disable server-side archiving (it's on by default in most modern implementations).