What Is It
Post Social is a physical social media platform that invites users to interact with each other through letter posts.
Fyi, it is not chain mail :)
Why
The idea behind Post Social is to generate a tactile connection between friends. This might be new for some or a blast from the past for others. Either way, it seems our world is largely digital, and bringing a physical element into our lives could help slow things down, and allow us to enjoy the moment just a little more.
How It Works (Post Creator)
Download the template for your post and print it out.
It fits an 8.5" x 11" piece of paper (landscape).
Folded fits a standard letter envelope. 
Ask anyone you would like to send the post to for their mailing address. Be sure to tell them your plan and ask if it is ok that their address will be listed along side others (if you plan on sending the post to more than one person). We share our information in all kinds of places but best to get permission here and have everyone on the same comfort level.
Fill in the addresses with those of your friends. The order of the addresses is the same order that your post is mailed. Put your address last so the post will get mailed back to you. If you leave some address spaces empty cross them out somehow for the receiver(s) to know it was intentional.
Create your post. It should be hand written. Add media (if you want). Stick figure drawings are more than acceptable. It's up to your own imagination what to put there. Taping or gluing other work is also acceptable.
The posts can be light and simple, like "I just had this noodle bowl for lunch" (included with a bad sketch of the noodle bowl). Or, they can be as personal and nuanced as you wish.
Once your post is complete, mail the letter to first address in your list.
How It Works (Post Receiver)
If you receive a post (lucky you :), take the time to enjoy the post and tactile experience.
Once you have absorbed the full extent of the post, create a reply in the first Reply space available. Where you reply should correspond to your address number. This helps the poster know which reply belongs to who.
Once you have replied, mail the letter to the address immediately following yours. 
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Hopefully, the original poster gets their post back. Keep it, don't keep it, scrap book it, tuck it away in a drawer. It is your post to do what you want. If it was fun, maybe there will be more :)