Contrary to reports that say IE 6 is dead, unfortunately it is not. Today I got an urgent call to come help an outside technician that was installing a new remote support tool on some equipment. He was having problems because he couldn't get past our IronPort WSA web filter. I trotted up expecting to just add a few device IPs temporarily to the proxy bypass list until he was done downloading things. Unfortunately the application needed web access all of the time and used the installed version of IE which of course was IE 6. This is where it gets hairy.
Ironport WSA is configured to use passthrough NTLM authentication to authenticate users for Internet access. This works great for IE 7+, Firefox and Chrome. Unfortunately IE6 is braindead when it comes to NTLM authentication and only works with some NTLM proxies. This means that I have to hard code any IE6 clients to use our proxy explicitly.
Moral of the story, vendors please update your "appliances" to modern software versions.