I'm not sure why this is getting downvoted. I love email and I'm sure I'll be using it in the retirement home. But it is not very popular among the youth:
And there's good reason for that. Email is basically the electronic equivalent of postal mail, a first pass at digital communication that aped the old medium. But the first email RFC was 35 years ago. MIME is more than 20 years old, and that's the last major capability improvement.
From the point of view of a teen who grew up on Facebook Messenger, Snapchat, Instagram, and Twitter, email is weird, old, and feature-deficient. They think of email in the way that I think of paper mail (mainly for formal and commercial use, not really for friends, somewhat quaint), or possibly how I think of a fax machine (quirky, obsolete, use only when forced).
Voicemail was very popular in the US for an extended period. Email becoming popular helped reduce that; so, later, did texting, especially once we got past the T9 keyboard.
The only people who leave me voice messages in 2018 are unsolicited job ‘recruiters’ here in London. It’s guranteed when I have a voice mail it’s them, like it’s 1998.
I'm currently in a country where access to social network sites like facebook, instagramm & twitter is being blocked for two days due to political issues (Sri Lanka). One fellow travel (21yo) does not know how to reach out to any of his friends and family besides using facebook & whatsapp. Sadly, he didn't even think of using email to reach out, even though everyone has one. Can't blame him for not knowing about VPN and TOR. So, reality is that we're (still) living in times when a simple, reliable and independent service like email does have it's advantages and can be very useful from time to time, esp when travelling or when politics change.
What doesn't work great about email? easy to use, easy to set up, easy to modify, easy to switch which software handles your email both server-side and client-side....
But people posting tonnes of GIFs, emojis, and tagging @all on #general isn't spam? I don't disagree that email has a spam problem (though spam filters have gotten quite good in the past 20-30 years), just that spam isn't an email problem.
It's trivial to ban someone from Slack. The problem with email is how there's no authentication for incoming mail, and it's trivial to spoof the sending address so you can't block them. Sure spam is a problem on most platforms, but unauthenticated ones have it orders of magnitude worse than authenticated ones.
Every submission system has a spam problem. How is email any different?
I'd actually argue that email is one of the better systems, as I can manage and control my whitelist/blacklist myself. It makes things much more functional that way.
Nobody does, sadly.
Baking it into the protocol like Signal and WhatsApp did means nobody has to want it, they just get it included without having to bolt on any extras.