sam_lowry_ parent
This is why they provide a choice to use their own servers
Then why implement email as a backend if email cannot actually be used as a backend?
That's the tricky part of having email as backbone technology. It's an old and varied ecosystem.
I host my own email server and I am pretty sure chats will be instant with it as well as with their servers.
However, some email providers implement various throttling mechanisms.
If you are OK waiting for message to arrive or be dropped silently, you may continue to use Google and Microsoft email.