When we look back, I think we will see that in abandoning email as the medium of social interaction, we basically gave up on the open internet.
People in various compromised situations use it because it doesn't need a phone number (unlike a rapidly growing amount of social networks.) I've set up dates over email, most of my work is done over email. I tell people to email me rather than text me because I am /much/ more likely to get an email (and get it quickly, thanks to IMAP IDLE.) It's the only thing I get notifications for on my laptop and the only thing I reliably get notifications for on my phone.
It's not abandoned, it's just not as hip as snapchat.
An only tangentially related anecdote: SMTP and later XMPP offered beautifully portable social graphs. In fact, in 2012, I found it so portable that I decided to migrate off the self-hosted postfix/dovecot/ejabberd install I'd run on my own domain for years to GApps. Cue the replacement of GTalk with Hangouts, and now I really don't have much of a choice but to pay Google each month, or discard/re-establish the social connections I've built over the last decade and a half.
A) Wide global adoption
B) Decades of use
HTTP?
I'm not sure of your point. Http also allows you to identify the server. Forwarding mail servers are analogous to caching and forwarding proxies.
> other metadata and separate them from the message
Just like http.
> HTTP is just "this is the filename, this is the data.." It's not much more than a TCP stream really
No, it isn't. No more than SMTP, IMAP, and pop3 are.
What's the difference? An email address isn't a person, nor does it represent one.
> I truly don't understand why you're on about servers and transport protocols when this thread is about social networks.
Because it was mentioned that SMTP is the only decentralized protocol, and I disagreed.