A department couldn't send email farther than about 500 miles

The case of the 500-mile emailTrey Harris / ibiblio.org, 2002

The chairman of a university statistics department called to say that email could not be sent farther than about 500 miles, and that his staff had drawn a map to prove it. The administrator was sure email does not work that way. Then he sent test messages to servers at different distances and found the same boundary. The story follows how he worked out why distance could matter to a mail server, down to a calculation that explains the number itself.