When you send someone an email and you get a strange email back that says your email didn’t make it through, don’t just stop there. The recipient might need your help in order to receive emails. Especially if their mailbox is full.

Typically, a bounce message will contain several pieces of information to help the original sender in understanding the reason his message was not delivered:
The date and time the message was bounced,
The identity of the mail server that bounced it,
The reason that it was bounced (e.g. user unknown or mailbox full),
The headers of the bounced message, and
Some or all of the content of the bounced message.

The important piece of information is the reason. Perhaps that person’s mailbox is full and they need to be informed of that so they can clear out some old emails.