We wish to limit the number of emails a subscriber can receive in a given time period. Eg Subscribers can only receive 3 emails in a fortnight - if at the time of a send any subscribers have received this number of emails in the set period they are excluded from the send list, those subscribers who have received less are included in the send list. Is there a setting that allows for this?
You will want to get Audience Exclusion scripts enabled under your account (not standard), and write a 1 line exclusion script to check a DE to see if there are more than 3 emails sent in that given period (you could also query the _sent view or sendlog, etc.). Have a look at my answer here.