Here is an svg template for cutting a box to hold A2 cards and envelopes. The original design for this came from here. Set the height at 7.5 inches for A2 envelopes. I have updated the file with score lines in a separate layer.
This file is for personal use only. Feel free to link to this post, but the file is not to be shared or distributed in any way.
The download is a zipped file containing a layered svg file. Download the file from here.