Can be deleted. "Hill Mailbox" APP is a software that can be used in anonymous society. It communicates on some topics by writing letters, and random strangers see the information. The information sent by this software can be deleted. Just open the Personal Center and select the letter you want to delete. A mailbox is a box set up by the post office for people to send letters. It is opened and collected by the postman on time and sent to the post office for mailing.