This format comes from older standards of formal invitation etiquette, when using courtesy titles was much more common. Including the first letter allowed guests to complete their preferred title themselves while maintaining the formal appearance of the RSVP card. Modern invitations, however, have become more flexible.

Guests who do not use traditional courtesy titles do not need to feel restricted by the “M.” They can write the title they normally use or simply provide their name, depending on the space and instructions. The main purpose of the line is identifying who is responding, rather than forcing someone to use a particular title.