> domain names were not handled properly by some versions of IE running on intranet Your choice of words implies there was a bug in IE, but there likely was no

> domain names were not handled properly by some versions of IE running on intranet Your choice of words implies there was a bug in IE, but there likely was not. People quickly forget before Google dumbed down the landscape with its Unibrowser and forced its ways and whims upon the world (and continue to do so)... IE had user-accessible settings for EVERYTHING. IE also had the concept of security zones with different settings for each zone including Intranet, a feature ahead of its time - quirkily enough and nearly undocumented, Chrome on Windows quietly uses IE's security zones for a few purposes of its own. Indeed, there are separate settings in IE for "Send IDN host names for [non] Intranet URLs" with different default values depending on Intranet or not, and the _ was likely interpreted as an international domain name and triggering this setting. Why does this setting exist? Knowing Microsoft almost surely for some backwards compatibility edge case.