In multiplayer, there should be mailboxes instead of using a /msg command. You can build a mailbox and you can receive mail from other players in your mailbox. You can use paper to write letters and create envelopes. When you use paper, you should be able to type on the paper so you will be able to mail it to someones mailbox. When you finish creating the letter, you put it in the envelope and right click on a mailbox while holding the envelope with letter in it. Also, in order to write letters, there should be feather pens, you make them by combining an ink pouch and a feather together to make an inked pen. And to make a mailbox, you can make it out of many materials, such as wood, stone, and any other types of metals.
So, what do you think of this suggestion?