The thing is, if you go to CCdungeon and finish at least the first floor, then you will get that email. If you take the item and click, it will give you a quest completed. You just have to deliver it to the NPC on the CCdungeon entrance and you will recieve 10LP and 10EP potions that you can use only inside CCdungeon.

Try to dont waste them, cause those potions are the only ones that works on the CCdungeon.