退信这是什么原因

seikorose

请问以下退信是什么原因
From: MAILER-DAEMON@telenet-ops.be (Mail Delivery System)
To: XXXX@XXXX.cn
Date: Mon,  3 Dec 2007 10:52:10 +0100 (CET)
Subject: Undelivered Mail Returned to Sender


This is the Postfix program at host in-mx1.telenet-ops.be.

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 Postfix program

<hongmei@inno.com>: host gakh.inno.com[212.123.30.53] said: 550 Requested
    action not taken: mailbox unavailable (in reply to RCPT TO command)

goxia

对方邮箱无效

leonuk

550 Requested
    action not taken: mailbox unavailable (in reply to RCPT TO command

就这个一句就好了。