Because 163 mailbox has a very useful function (you can set "read receipt"). If the tutor reads your email and doesn't reply to you, the system will automatically send you a "read receipt" to let you know that the tutor read your email.
Changing majors means changing to other majors. In order to complete the enrollment plan, colleges and universities need to transfer the losers of their volunteer majors to majors with unsatisfactory enrollment. Therefore, when volunteering to fill in the form, they designed the subject adjustment column, and the candidates voluntarily chose whether to obey the adjustment. When all the majors reported by candidates cannot be admitted, if they choose to be transferred to other majors, they may be transferred to other majors.