I have set up an Auto Response but every time someone sends me mail they get five copies of the auto response instead of just one.
You have probably set up a message loop by typing in your own e-mail address on the "Edit Auto Response" screen.

The e-mail address on the "Edit Auto Response" screen should only be used if you want messages forwarded to somebody other than yourself (i.e., a different e-mail address) in your absence. Clear the e-mail address field and press the Save button.