missmandimichelle answered your post:

you can, but it won’t be recognized by the post office unless it’s in the top left corner on the front.

legslaceandsunnydays answered your post:

I believe that you can, however normal practice is top left corner. try looking at FAQ on the website of whatever mail service you’re using!

My matron of honor works with a printing company and she said that they print them on the back all of the time and don’t have any trouble. I’m just doing plain jane local postal service.

Why won’t it be recognized? I don’t get that.