プロバのアドレスで自分にテスト送信しみたらこんなのがくる
翻訳サイトで見てみたけど意味がよく解からない
今までは使えていたのになあ？

This is the Postfix program at host mail.asahi-net.or.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