Need to send a message to a player for them to see later? Mail is a good way to get that taken care of.
You can access your mail from by clicking on the "Mail" button from the Life Skill menu in the bottom-right of your screen. Your mailbox can also be accessed by pressing the default key "O".
From the mailbox, click on Compose Mail to begin.
In the Compose Mail window that opens, type in the name of the person who will receive the mail, the title for your mail, and the whatever you would like in your message. Clicking "Send" will send that message to the recipient.