Make sure to check with the post office or courier service how the ball is being sent. If it is being sent via air (international & interstate), it is essential to deflate the ball as the added air pressure can force the bladder to expand and potentially damage the stitching of your football.
If shipping internationally you must deflate the ball. If you don't you not only risk the ball being damaged but your package may not be allowed through customs and you will need to pay for shipping twice.