Gregory's Server@delta Delta chat is a very good messenger. I love it. The only drawback I have compared to xmpp messengers is that it does not support audio and video calls. I know this is difficult with emails, but if somehow you could make a calling sound when somebody calls to a jitsi video meeting ID that is already registered with Delta chat account.
@madsee34583 there already is jitsi integration if you configure a base url in advanced settings but indeed no calling sound / ring yet when you receive a call invitation. And thanks for the positive feedback, much appreciated!