What happens if I change my smart sending window after I've already scheduled a campaign that's using smart sending? Will the new smart sending window be recognized?
Smart sending is applied to a profile at the moment they receive an email. When they receive that email, a timer starts based on the smart sending window that is currently in place. Changing the smart sending window within your settings does not affect the timer that may already be applied to profiles that are included in a campaign you previously scheduled. This means that if the existing scheduled campaign is going to send within the previously set smart sending window, and those targeted profiles had received an email within that time frame, they will get skipped due to smart sending. The only exception for this is if the campaign that's schedule has "Use Smart Sending" unchecked.