I mentioned the “locked” letter that Thomas W. sent to me in yesterday’s post, and there was curiosity on how such a thing is done. Here I have reverse-engineered the process from his example. 
Take an 8 1/2″ X 11″ sheet of paper and lightly fold in half along the 11″ side, creasing the center edges for reference. 
Open the sheet again, and then fold in the upper left and lower right corners to the marked center of the sheet. 
Fold in the right and left edges flush with the previous fold edge. 
Fold in top right corner and bottom left corner. 
Tuck corners into pockets. 
Seal the back with a long label or strip of tape. 
Address the front center and apply stamp to upper right corner. 
Currently in the earholes: 
EDIT: Oh hey, Youtube reminded me that Joe VC did a video on this method about a year ago, check it out!
Cool!
Member Mike A. folds his letters in a different, more square technique.
It’s fun to rediscover these stationery tricks!
Cool letter origami!
Medieval times had a lot of cool and intricate letter locking mechanisms. Specifically designed to be unable to open the letter without damaging the “lock”, so you could see that the letter had been tampered with. Here’s an example: https://www.youtube.com/watch?v=U3lGlmRPMKw
Excellent! (: