See also SMTP which has flooded the Internet with huge amounts of garbage traffic but which is simple and works well enough that any alternatives fail.
I agree with your main point, but I wanted to add that there are plenty of alternatives to sending e-mails using SMTP these days. They mostly go by names like "Facebook" or "Google+" and run over protocols like HTTPS talking to a centralised service provider, and they solve the fundamental problem -- letting people send text and picture messages to friends/colleagues for viewing at their own convenience -- in a different and mostly incompatible way.
Of course anyone who needs reliability and privacy will question the use of the specific public social networks I mentioned as examples, but the same principle applies when businesses deploy centralised in-house systems. They still handle messaging (and often a lot more besides) for their key functions using dedicated tools, so general purpose e-mail is no longer necessary for those functions. Increasingly these organisations also use VPNs to allow employees and other associates who are not physically present to hook into the same centralised systems remotely.
Sure, but I think you would be hard pressed to find a company that didn't have some form of email system for dealing without people outside of the company etc even if internal communication is done by some other tool. It's a network effects problem, you could build a better email system but you can't get rid of email completely until it's as commonly used as email.
Such a common tool needs to be highly resilient to catastrophic failure in the same way email is.
For example the DDOS on sendgrid affected sendgrid and their customers but the rest of us were unaffected.
The implications of a system that allowed groups like Anonymous to cripple worldwide trade at will via DDOS would be quite scary.
I agree with this too. I'm not suggesting that e-mail is dead or anything, just that a lot of use cases aren't so much being replaced by an alternative to SMTP as being replaced by another communication channel entirely.
I agree with your main point, but I wanted to add that there are plenty of alternatives to sending e-mails using SMTP these days. They mostly go by names like "Facebook" or "Google+" and run over protocols like HTTPS talking to a centralised service provider, and they solve the fundamental problem -- letting people send text and picture messages to friends/colleagues for viewing at their own convenience -- in a different and mostly incompatible way.