Cannon you plonker!
Customer: "Hi Pete, can you arrange for the mail to be put back on the original IP?" Me: "Sure, hey I know, lets check it's working first?" Customer: "Good idea." Me: "Nope .66 .69 or .71 is not accepting telnet connections." Customer: "That's strange? I'm sure it was .71 tbh." Me: "Oh" Customer: "What?" Me: "Helps if you put the port number on doesn't it?" Customer: "Just a bit."