Gmail is the email solution of choice for a huge number of Netizens, and that provides a rich playing field for developers hoping to be useful to you by providing tools that simplify email overflow.
Enter Google with its latest endeavor, "Inbox." From Engadget:
If you're anything like us, Google's Gmail has an iron grip on your life. Google's looking to create a whole new iron grip with a new app from its Gmail team, and it's called "Inbox." What is it? That's a good question -- Google's made a demo slash advertisement video that we've dropped below. As far as we can tell, Inbox is a combination of Google Now and your Gmail inbox -- a "smart" inbox, if you will. It combines alike pieces of email (bank invoices, for example), highlights related information (like Google Now alerting you to flight changes, traffic, etc.) and keeps track of your life (it'll give you reminders, among other heads ups). Is this the end of Gmail? We seriously doubt it, but it is Google's latest foray into simplifying email.
They've pissed around with the UI ever since then and generally made it into a beast that's less likeable by those who value their email. It might have helped folks that oversubscribed to junk or facebook status updates and didn't know how to create filters to deal with all of it. But to serious emailers the changes were annoyances.
Shout-out, by the way, to Fastmail.com, who does nothing but IMAP and does it right. I don't often use their web interface because I'm a email-client kind of person, but when I do I find it easy to manage and not too "fruity."