Hi, i m serious freelancer with 100% completion rate and i believe i can do this for you. As far as i understand you, you already sent 7000 emails (and you have a list of those 7000 email accounts). Now your coworker sent you 16000 email accounts and you don't want to sent duplicate emails. So you want to get email accounts from those 16000 that are not already sent. Basically i would create a macro that loops through those 16000 email accounts and for each email account check if its already in those 7000. If it is: skip it (this means that mail is already sent), if its not put it in a new list (this means that mail is not already sent). If you are interested you can sent me a list of for example 50 mails (new list) and 10 mails (old list) and i will create you a macro to find you a difference. And macro will be able to work with any number of email accounts. So if you are interested please message me. Thanks Milan.