And there is no ability to delete messages on the server, at all. How is this usable? Chats will completely spam Thunderbird etc. and they are not deleted.

You have a few options with DeltaChat to delete old messages.

• Use the disappearing messages option : https://delta.chat/en/help#ephemeralmsgs
• Go to the settings and choose to delete from device and server : https://delta.chat/en/help#what-happens-if-i-turn-on-delete-old-messages-from-server Then you can also delete messages in the chat windows by right clicking on them.