How to frost cookies that will be mailed?

Use a royal icing, and let dry completely before packing.

@PandoraBoxx Does it harden pretty well?

Yes, this is what is used to put the details on gingerbread men so as long as you give it enough time to completely air dry before packing.

The enemy here is moisture.

You could also put some waxed paper between the layers rather than plastic wrap which tends to trap moisture.

Well the ship time would be about three days between my house and his. We don’t live but an hour away. Hopefully they’ll hold up between then. eek

I was also going to say royal icing. It’s what we used to use for Christams cookies being sent to relatives at Christmas. However, we always used milk instead of egg white or meringue powder. You can mix in all sorts of colors and flavors as well. I know one year my brother insisted on using rootbeer extract for some reason. Generally, almond, vanilla, or lemon extract work best.

Here is an official recipe, although we never used the corn syrup either, just milk, powdered sugar, coloring and flavoring. It dries to a hard surface, and if you are worried, as @Buttonstc says, you could put wax paper or even tissue paper between the layers. However, unless the package gets caught in the rain the icing should survive a three-day postal trip just fine.

Try Cheryl and Company. A variety of frosted cookies will arrive in perfect shape and taste great.

@galileogirl Yeaaaah but I really want to hand make them. :P

We used to just use icing sugar and milk/water and colouring. If I remember my gingerbread houses doesn’t royal icing dry to toothchippedness?