Email Preference Center

You could use a global suppression list linked up to a smart Campaign. 

Something like,,,

If they have been emailed (x amount of times in xx amount of time) Add them to your suppression list (blacklist unsubscribe... whatever) If not. Do nothing. 

I might recommend setting up a suppression list used agent’s future campaigns. 

Thats more of a global solution. If you wanted to go to just one person filter by their email address.. Email was delivered (is any) add contraint Min number of times. 
 

Okay, I think I can see that working. I would set up lists with members that meet emailing frequency criteria. Then when running campaigns, add each of the profiles as list members to exclude if sent X amont of times in XX amount of time). Is that what you had in mind?

Thanks for responding. Needed to approach from a new angle.

Sure. I would encourage you to do this on more of a global level with a standard filter criteria. Or else it's going to be a pain to make all the lists.  One list used for suppressing people would be ideal. But thanks to Marketo you have a lot of options when it comes to this and customization! I came from Pardot and I can tell you this is so much better!
Best of luck! I think you’re on the right track. Let me know if you need any more “out of the box” ideas :)