If you dream of writing letter, it can mean you have some important communication to pass on. This type of dream is usually a reminder to do your “homework” and get your necessary work done.
If you can see yourself writing an email, or composing a letter at your computer, this imagery gives some clues. To be using a computer can mean the writing is to be sent to a formal contact. On the other hand, to be using a pen to write means the communication is to be sent as an informal message. This could be a short note, or an informal letter to a friendly acquaintance.
Sometimes, writing a message can be directed to the dreamer’s self. Maybe the subconsciousness has a message to pass on to the dreamer’s consciousness. It’s important to record dreams to prevent their loss due to short term memory displacement in the busyness of the day.