Thank you for sharing your feedback on a feature like this! The good news is our development teams has added the ability to filter contacts based on their activity with your emails. Have you tried using our segment feature? This feature will allow you to create segments of your contacts based on not opening any of your last 5 emails, a specific email, or any email. These contacts can then be added into a new list, and sent a follow-up email like this. I hope this helps.
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