If you served http://example.com/foo.msg http://example.com/foo.msg as text/plain, older IE versions used to helpfully assume the user wanted to view it in Outl

If you served http://example.com/foo.msg http://example.com/foo.msg as text/plain, older IE versions used to helpfully assume the user wanted to view it in Outlook Express, which exploded because it only supported some binary monstrosity and not text/plain. Dots are not special in an abs_path, and you can't make an interoperable network by assuming your peer does everything the same way you do.