Thank you for your response. I was actually unaware of this point ' Only people with images enabled will ever log an open'.
Yes, Opened Mail must use a tracking pixel.
Would it be best to only ever send resends with a different subject line and to those who haven't 'clicked on links'?
I tend to agree with Michael that resending a (non-operational) email without any changes to the body creative is a bad idea. But sending only to people who didn't click and didn't open at least narrows the field of people you're sending it to.
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