This script compares a list of emails you want to make sure are included in a campaign against an existing master list, creates a list of those that are missing in the master and tells you how many unique emails are missing.
I have used it to ensure that my VIPs are included in relevant email campaigns, at times when better alternatives weren't available.
It assumes both lists are on separate csv files with the emails in a column named "EMAIL".
For now, I am marking the file paths as "add_your_file_path_here.csv"