postfixでメールスプール（メールボックス）がいっぱいになった場合に
送られてくるメール
This is the mail system at host mailhost.adf.co.jp.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
The mail system
writing message: File too large
sendmailだとこんな感じ？
Message size exceeds remaining quota/over quota
