Parchment

In the mud world, characters can send tells or whispers to one another. In
addition, folks may send letters via carrier pigeon. Paper to write notes on
must be purchased, penned, sealed, and sent to the receiver.

Example of a common letter writing sequence.

Buy paper.
Write This is my letter to you. Signed, Me.
Seal paper
Sendto ThatPerson letter

The letter is then removed from the sender and placed in the receiver’s hands.
The reciver should then –

Unseal letter
Read letter

After that the letter is useless and may be discarded.