in reply to Tülsa

DC has a local database. It fetches messages via IMAP and sends messages via SMTP.
After DC downloaded emails from IMAP you can delete them there and they still stay in the app, because IMAP is only used as transport, the chat messages stay in the local database.

It is basically a fancy email client, like Thunderbird, just with a chat ui and different features.

each message in deltachat is an email