Below is the text you can read from within the message.
Welcome to Kethsi. I'm sorry that I have no means of knowing your name. I don't have much time before the magic takes hold and my reincarnation takes place.
I also enclose a note to myself, which you must give me when you see me, but NOT as a cat.
I enclose a necklace crafted by my sweetheart, Ilsinor. there is no other like it. You will need it to convince me that the note I sent myself is worth remembering.
There is information on this island that will be needed if the enemy is not to overtake us all. It's protected by an ancient Kethsian puzzle. I enclose vital items to help you complete that puzzle. I hid them here many years ago to keep them from getting into the wrong hands.
-Robert the Strong
P.S. DKQ is a code which could become useful to you at some point.
After completion of the associated quest, if you have unlocked the entire Hub track, this item can be retrieved from the Quest Item Storage chest at the Quest Point Caravan if lost or destroyed. Otherwise, a new one can be obtained from searching the wall again.
There is no need to keep this item after the quest has been completed. As such, it can be destroyed or kept as you desire.