Update: Nov. 30
Further experimentation (by chance, with a new laptop set up by Geek Squad for travel) shows that the IIS has trouble if the user enters or clicks on a url that requires translation of the "www". That is "http://doaskdotell.com/movies" will work when "http://www.doaskdotell.com/movies" sometimes gives a service unavailable or connection refused. This sort of thing used to happen before 2000 on some servers.
Update: Dec. 25
The site "Bobcares" explains the complexity of IIS application pools and users that can cause 503 errors, here.
It sounds logical that problems could occur fending off DDOS attacks and botnets, but the topic is complicated, as in this Microsoft reference.