I would say mail him something he likes. Find that out by asking him what his hobbies are. If he collects cards, for example, get him one he doesn't have.

If you are good with arts and crafts, you could make him a scarf, a shirt, an ornament, a card, etc.

Since Valentine's day is coming up, you may or may not have time to send something over mail.

You could create an electronic card for him if you know how to make graphics.