Email as we know it has had its time.
One of the biggest problems we face today is our overflowing inbox. The way we use email (reply, reply all, cc, bcc, forward) is just asking for trouble. A conversation should become simple again.
And you might think it's just a matter of tooling. Some apps already do a great job. But actually, they're just hacking the system, as the problem lies deeper.
From a technical point of view, email is very simple, as the name of the protocol already suggests (SMTP: Simple Mail Transfer Protocol). Everything is transmitted as pure text. As a consequence, every mail can be read on every server your email passes. So your privacy is at risk.
The recent Snowden revelations about the NSA practices are a proof of what's technical possible.
Secondly, when binary files are attached to an email, they are converted into text files making them on average 33% bigger.
Emails are still hopping from server to server to reach their destination. A good idea in the old days when servers weren't very reliable, but today it's just a waste of costly resources.