I did something similar: I made a little Javascript web game which you have to play and win in order to RSVP. Made a spreadsheet of guests and their emails, and

I did something similar: I made a little Javascript web game which you have to play and win in order to RSVP. Made a spreadsheet of guests and their emails, and emailed them all using the Mail Merge extension for Google Sheets. Once you play and win the game, it links to a Google Form with your name pre-filled. All the responses go into a spreadsheet, and I can easily do a query against the original spreadsheet to see who still needs to RSVP. Then follow up with those people personally. Overall people really enjoyed the game and thought it was a unique invite. Plus it saved a crapton of money and trees and gasoline, which was the most important part for me. The wedding industry is built on waste and my fiance and I don't want to support such an outdated, unsustainable tradition.