Everyone likes to get mail; as in an actual letter in the mail box. It feels so much more personal than those quick shot messages through the internet or by text. Here's a few ideas to include your kids in on this time honored tradition.
Start them young, even before writing age by having them draw a picture for mom or dad and 'mailing' it. This could be as easy as putting it under their pillow or actually helping them put it in the mail box. And of course the best part is when you get a response so make sure to send a special note or picture back.
If you want to step it up a notch, make your own mail box out of cardboard for your special delivery!
Or check out these two from the brand Melissa and Doug for play practice of writing and sending post!
Make your letters interesting by decorating the envelopes! These are made from pages of old children's story books.
And this is a sample of the letters Maurice Sendak the illustrator would sent. Just a little inspiration...How fun would that be to get in the mail?!
If you really want to make correspondence a priority in your house, consider installing a letterbox in the playroom or outside your child's door to encourage back and forth communication. 
One of the coolest gift ideas I saw out there was a friend who gave twelve pre-addressed and stamped envelopes with note cards. The idea is to write or draw highlights from your month and send it to your friend and they write on the back of the note card and send it back. In the end, you have 12 months of correspondence. This is a gift that keeps giving with the anticipation of a new card each month and it also helps develop letter writing skills.
Snail mail might not be as popular as in the past but it's definitely a valid art form and teaching your kids how to use it is a life long skill. Plus, it's lots of fun!