IE8 and older to be specific[0]. But, if you're supporting IE8 still you have bigger problems at hand.
Microsoft stopped supporting any version lower than IE11 as of January 12th of this year[1]. So unless all of those older IE machines are accessing an intranet (and only an intranet) their risk of being hit with malware is way higher than average.
For my clients I do a cursory IE9+ review, but if anything lower is a requirement then it's an additional fee to make a site work with it.
In a few months it'll be IE11+ and the same fee structure will apply to anything lower (I'm just waiting for IE10 to wind down a bit).
What I do, is provide nwjs to those on old versions, so they think they are getting the "application" version, but in reality, its Chromium hard coded to only goto the web application.
So far its a win for both parties, since they are not installing another browser than can interfere with some silly IE6 only internal enterprise site and we get to use the latest browser features.
Believe me, I understand how comments like that get on one's nerves. But civil discourse requires those of us with nerves to tolerate the irritation enough not to toss it back. The system has no steady state: the irritation either grows or we dampen it.
