We launched a web application for construction companies in Switzerland a few months ago. And quickly learned the hard way that we have to improve the IE compatibility. The last 90 days IE11 was used for 36% of all traffic.
Too bad the new Edge isn't called IE12 and automatically deployed as a replacement through Windows Update :-)
I'm fairly sure Microsoft is not fan of IE either, but they will still be stuck with it for many years. The most they can probably do, is to not have it installed by default in future versions of Windows 10, but I have a feeling that it will stick around for longer than IE6.
I would love to use CSS Grid without thinking whether it will work however it happens that IE11 has only partial (and buggy) support for it.
I believe that supporting IE11 blocks innovation.
So, what is the use case here really, what sort of features IE11 does not provide that you'd need to implement a web-based mail client?
(note that i'm not trying to promote IE11 here, i just do not understand why IE11 would block implementing any feature to the point of dropping it entirely)
A world where Blink has 80%+ marketshare (which is pretty much what we have or where we're headed) is one where a single group can dictate the standard for everyone else.
Having said that, IE11 is still supported so it doesn't strike me as security risk. In fact, not updating a browser with features is likely going to improve security. A little-used browser is also less attractive to target for exploitation.
At my company we're in this weird spot where Chrome has overwhelming adoption but IE11 has more usage than some of the other modern browsers. For example, if we only went by usage (or even more so: conversion/$$$), we'd be dropping Firefox support before we drop IE11.
That obviously doesn't feel great. I don't want to be in a "This website is optimized for Chrome in 2560x1440 resolution and 32 bit colors!", reminiscent of the old Netscape vs IE days. But we're getting very close to it. Firefox's usage is dwindling. Safari is pretty bad at anything except saving battery. Chrome is good but Google is pretty sketchy with how they bully their feature requests into the standards. IE11 can go to hell, but I still want people to test across browsers. It's happening less and less.
Have you tried contacting their support team?