Correct MIME Type for favicon.ico?

Question

According to the Internet Assigned Numbers Authority (IANA), all .ico file falls under the MIME type image/vnd.microsoft.icon. (Source)

E.g

Answer 1

I think the root for this confusion is well explained in this wikipedia article.

While the IANA-registered MIME type for ICO files is image/vnd.microsoft.icon, it was submitted to IANA in 2003 by a third party and is not recognised by Microsoft software, which uses image/x-icon instead.

If even the inventor of the ICO format does not use the official MIME type, I will use image/x-icon, too.