This box ended up being one of those "happy accidents." I was adapting the measurements from a smaller box to fit my needs, but my paper wasn't long enough for the box to completely close upon itself. I decided to try adding a brad and some ribbon to make a latch. This box easily fits six A2 envelopes and six 4 1/4 x 5 1/2 cards.
Begin with a piece of cardstock cut at 8 inches x 11 inches.
With the paper turned vertically, score the paper at the 1 inch and 7 inch marks. Turn the paper horizontally and score it at the 1 inch, 5 1/2 inch and 6 1/2 inch marks.
Cut along the score lines as shown, and add adhesive to the flaps.
Assemble the box as shown.
To keep the box closed, I added a brad and ribbon before embellishing the box. You can see the finished box here. If you want a box that closes completely, begin with an 8x12 piece of cardstock. In addition to the instructions for this box, you will also score the paper horizontally at the 11 inch mark.
I think these make great gifts!