I will be sending my library book back by mail. It will not reach the library by the due date. I cannot renew it again.
Books mailed or sent by UPS to the library are checked in by the date the package was sent; not by the date the package is received. So, you won't be charged overdue fines for transit time, even if the package arrives after the original due date.
Contact your campus librarians for further details on this.