Nor does Delta. Nobody will “chat” with me via their Gmail email focused UI, so it’s effectively a separate network anyway.

Using an email address as an identifier for IM is a great idea (I hate that everything uses phone numbers for this, which are not internationally portable and not possible to reasonably “self-custody” the way TLDs are).

But using the actual email protocol as a backing protocol for instant messaging seems like a weird contortion and still makes this effectively a separate protocol, the split being servers that do and don’t support all necessary extensions. The overhead must also be staggering; just look at an email header to see how much is going on for each message these days.

you got a point with the overhead in email headers. also an email is sent not only for every message but also status updates. that adds up to a lot of emails.