To avoid repeating rules several times when a similar message is received from the same contact, the Pause rule for… option can be used to implement a cooldown and pause the rule after execution.
AutoResponder remembers for each rule and contact separately when it was last executed.
You can find the Pause rule for… option at the bottom of each rule and decide between x seconds, minutes, hours, days or pause for the next x messages received from a contact.
Set something like 99999 days to pause forever if a rule should be executed only once for each contact.