Ask HN: How do you deal with Internet Explorer?

We're building a web application and are finding out all browsers behave normally, but IE. Internet Explorer refuses to open our pages.

Using Fiddler, we see we receive a perfectly valid HTTP request, and answer a proper HTTP response with a valid HTML page.

Nonetheless, IE (11) keeps answering "This page can't be displayed".

How did you deal with this? Do you still test and support IE?