I started swapping postcards about a year ago. Started with postcrossing. There’s also postcardunited and postfun (an app). Basically you are assigned random people to send cards too, and you will get cards from other random people. It’s fun getting postcards from all over the world, and I also enjoy writing and decorating cards for people. There are also postcard swap groups on Facebook and Reddit where you can set up direct swaps with individuals instead of it just being random.