As almost everyone knows by this point, the Internet Explorer maintenance GPO is a thing of past. If you want to set settings within IE 11, you are doing so via the Group Policy Preferences page. Much has been written about the red and green squiggly lines, what they mean, and how to change them (see here).
One day recently I discovered that the proxy setting for one of our IE 11 installations that had previously worked without issue had decided to simply stop working. The GPO that contained the GPP was applying correctly, the settings were making it to the computer. They just weren’t having any effect. Viewing the results of Group Policy via either the modeling tools within Group Policy Management or with gpresults.exe on the client showed everything to be good. It just didn’t matter, nothing we did worked.
After MUCH Googling, testing, and yelling, I finally discovered that back in the Server 2003 days the proxy override setting had a limit of 256 characters. At first I moved on to other troubleshooting steps. But then I got to thinking, I’m editing a GPO on a Server 2012 R2 Domain Controller and applying it to a Server 2012 R2 Terminal Server. This limit has been increased at least once, maybe twice, between Server 2003 and Server 2012 R2. But….our domain and forest are still at Server 2003 functional level. Aha! It doesn’t matter (for this aspect) that the OS the GPO is created is the latest and greatest version. Nor does it matter that the OS it’s being applied to is the latest and greatest. It’s a Group Policy Object. It is intrinsically linked to the forest and domain.
We trimmed up the proxy override list. A couple sites could be removed completely, others were vastly shortened through the use of wildcards. We got it back under 256 characters, and BOOM. It instantly started working again.
Looks like we might have a reason to upgrade the domain and forest before Exchange 2016 arrives after all.