Content-Type: text/plain; format=flowed
Subject: Delivery failure, user's mailbox is full
From: "Mail Daemon"<postmaster@system>

Hi,
  I am sorry to tell you that <rcpt>'s mailbox is full, we cannot deliver any message into this mailbox, please try it later. Thank you!

Below is the original mail information:
   Time:    <time>
   From:    <from>
   To:      <rcpts>
   Subject: <subject>
   Parts:   <parts>
   Length:  <length>
