>>692送ってもエラーメッセージが戻ってきますが。
This is the Postfix program at host pop3.j-com.co.jp.

I'm sorry to have to inform you that the message returned below could not be delivered to one or more destinations.

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 message returned below.

The Postfix program

<mhirota@j-com.co.jp>: unknown user: "mhirota"