I have a site http://example.com how do you make a 404 page for subdomains that do not exist?e.g if I was to try and visit a-sub-domain-that-does-not-exist.stackexchange.com I get a 404 page.The default behavior for subdomains is that they don't resolve.  I would instead like to create a user-friendly not found page for them.
How do you make a 404 page for every non-existant subdomain?
subdomain;404