You could do multiple if you would like. Sometimes people send the first and say that this is our first attempt at reaching back out, after 2 more emails without a response we will officially opt you out of future emails. Then in a week or so send another, and one week after that send a final attempt.
The most important thing is that you do what you say and actually opt them out at the end of the campaign. Do not make it so they can receive another email from you unless they take action on their end to resubscribe.