The Internet works on cache system, meaning that it uses extra memory at each site in the world to hold backlogs of information until traffic jams during the busy times of the day, quiet down. It oftens holds extra unsent email when one of the sites passing the messages along becomes too busy or a receiving is too backed up. It is possible this unsent email is finally arriving at its destination. There is nothing anyone can do about this. This 'caching' is necessary. If your mailbox gets filled up and can no longer hold incoming mail, mail won't get rejected. It will be held temporarily in the preceding site and will be resent repeatedly over a period of time until your mailbox is able to receive mail again. Only after repeated tries or a set number of days will the email message be returned to the sender with an 'unable to send' message.