Sure, it's always nice to receive a mailed invitation, but the party throwers of yesteryear really knew how to make a guest feel wanted. They'd hand deliver formal invitations to each guest with an almost embarrassing amount of fanfare. We're talking horses, trumpets and a footman in formal garb.
Commit to your theme from the beginning with invitations printed on parchment paper, rolled into scrolls and tied with a jaunty pink grosgrain ribbon. Want to add the icing on the proverbial cake? Recruit your teenage son to dress up like a royal messenger and deliver them in character. It shouldn't take much to get him to do that. An extra half hour tacked onto his curfew should do the trick nicely.