No, there is no value in us re-creating the wheel when Mobile Phones have great mail clients and third parties are building then as well complete with EAS etc.
Again, we would not build an XMPP clients either because there are already so many available. On Android, I use Xabber.
Also, I like the new emClient on desktop which supports Exchange Web Services and also supports XMPP. We are working with emClient now to work out a few EWS issues we are seeing.
Writing a mail server and writing a mail client are VERY different beasts and why companies do one or the other... except for a company like Microsoft... although in my opinion they aren't doing either of them really well right now. Microsoft Outlook on a desktop is in really bad shape. I do like the Microsoft Outlook on Android and iPhone ....