So if you don't need to create an account, how do you know you're talking to who you think you're talking to?

You use your email provider's credentials to log into the app, which then creates an IMAP folder called delta-chat which houses all those conversations.

You'd verify it's your mom by starting a chat with "momoforollo@her.email" she'd verify it's you by making sure it's coming from "orollo@your.email"