I have recently purchased a Black Lion Salvage Kit and 10 Mystic Forge Stones and have not received it. Up until now, I had no problems retrieving items I had purchased or had mailed. It shows in my history that I had purchased the kit and stones, but does not show up in the mail.
EDIT: I somehow managed to fix this problem. I switched characters and deleted some mail. Even though it listed it as 9/10, the new mail popped up for me and I had received my items.