An excellent consideration. And I think the ever-annoying answer is “It Depends”. You will need to do a value assessment. This assessment may be for each email or program, depending on the audience and the content.

If you know certain recipients use this tech, create a suppression list for this group and suppress just the duplicate emails, or every other repeat, etc. Do a check to see if they are on the list and skip the email if they are. Certain industries (tech/medical/security) or company sizes (fortune 100) may be more likely to use the tech, so maybe exclude those segments from the duplicates.

Do click tracking as an additional test. Be aware that there are firewalls that follow links – zScaler for one, so this also isn’t a sure signal.

Assume that if they visited your website since the email send, they read your email and so squelch the duplicates if they are recently active on the website.

Change up the duplicate sends a bit. A lot of work, but if it’s in a long living engagement studio program, it could be worth the effort. This gives you a built in A/B test. If the repetitive email is getting a better open rate, maybe swap the order and send it first. Maybe the order really needs to be that way to get the lift in the later email because people see the prior subjects and skip them, but the later subject line is now really compelling because of what they saw first.

People kinda have a half expectation of marketing departments to be a bit annoying. If the email is written to look like it was coming from a human, be extra conservative with the repeat sends. We don’t want to make our named people look dumb or desperate. Anonymous marketing departments, OK, but not our people.

You can always try alternative methods to email to get that 2nd chance. CRM remarketing for example, instead of sending a second or third email, display ads to those addresses.