If you are going to mail only one jar of pickles, I suggest you first wrap the jar in bubble wrap, then place the jar into a box just about the size of the pickles. To ensure no breakage, place that box inside another box, which has been lined with bubble wrap. Make sure both boxes are sealed securely and mail your canned goodies.
If you are mailing more than one jar, I think you'd be safe doing what I just recommended but adding lots of wraps/layers of bubble wrap on/around the jars in the first box.
I used to ship a lot of antique china all over the world and no one ever received anything that was broken.
Good luck and congratulations to the lucky recipient of your canning skills.
"As a girl I had zero interest in the stove." - Julia Child
This is real inspiration. Look what Julia became!