The comments by Geoff Krajeski on the workflow above offer good thinking.
Also, if you are sending emails to people who didn't open the first email, then you should consider making some changes i.e. change the email subject, body copy or send them a different marketing asset altogether i.e. one that's likely to have higher value to the contact and which is also then means you aren't spamming them with the same content repeatedly.
.png)