When your webhost provides cpanel as your hosting panel, you might have seen a link called 'AutoResponders' under 'Mail' heading. These are one time autoresponders where the sender receives the message one time in response to his email.
Example: Let us say you are on vacation. You can create an autoresponder saying that. When a person sends an email to you, he/she will receive the message saying that you are on vacation.

Cpanel autorespondes has a simple feature that controls the autoresponder interval in hours ...
How?
Say you have set the 'Interval (hours)' to 8. John Doe sent you an email on Monday morning 10 A.M. He receives your autoresponder message saying that you are on vacation. After couple of hours, he sent another message. Cpanel won't send the vacation message again to John Doe. If John Doe sends third email at 7 P.M, then cpanel sends the message again as 8 hours have passed.
So this time interval (in hours) will stop sending the same message to a specific person for a certain period of time.