It's not just relatively older, e-mail is one of the oldest technologies on the net (we're talking 1960s technology here!)
Frankly, I wish it would die already as it's pretty much held together with ducttape:
* it's all transmitted via ASCII; so any binary attachments have to be base64 encoded that increases their file sizes by ~30%;
* transport encryption still isn't the norm (this is the 21st century, why the hell are we still sending stuff in clear text!?),
* there's no standard error responses meaning it's often guess work whether mail has been received or not
* there's no standard way of rendering HTML mail, so anyone sending mailshots has to revert back to a 1990's web developer mindset (ie assuming that everything doesn't render so resorting to HTML tables and hours of frustration).
* it's not real time / real time daemons are not standardised. (I'm not saying we need something like instant messengers, but it seems silly that we have a small handful of proprietary push systems (eg Exchange) and the rest of us normal users have to instead rely upon re-syncs every 5 minutes (which means a fresh set of handshakes as well). A persistent connection would make much more sense for a 21st century e-mail network.
There's been so many attempts to "fix" e-mail, but most have either missed the point (eg Google Wave) or just added yet more ducttape to the existing problem (eg pretty GUIs that change the way we interact with e-mail clients but without actually touching the core technology itself).
I might actually write my own mail server and client one day because it's becoming obvious that most people are happy with "good enough"