I have 3 comics available and I'd like to e-mail anyone who has bought one of them about my new comics, but I don't want to send multiple e-mails to the same people if they have bought more than one. As far as I can see there's no way to do this without grabbing all the email addresses of my purchasers and doing some Excel work to get a list together (which I'm not going to do as it probably breaks GDPR  etc).

Is there a solution I'm missing?