The mail with the item attached will remain in the mailbox for a maximum of 7 days. This is because all mail in the Transporter is deleted after a set time limit. So please be sure to check the character's mailbox as soon as possible, after an auction has ended.
Auction House mail is also deleted as soon as the item is obtained. If a mail has been read but the item is left attached, it is deleted within 24 hours. If the mail is unread, the mail will remain for 7 days, and deleted after.
With the Auction House and Transporter time limits, we recommend that users do not set items in the Auction House unless they are able to check the items within the time limit. 1 day auctions must be checked within 8 days, 3 day auctions in 10.
Any items left unchecked for longer than the times set will be permanently deleted and unable to be restored.