无法发送邮件到.de邮件，heelp？

Question

Reporting-MTA: dns; lvpmailfs1.vip.hr
X-Postfix-Queue-ID: 4545360041
X-Postfix-Sender: rfc822; shops@ibci.hr
Arrival-Date: Mon, 20 Apr 2015 12:35:14 +0200 (CEST)

Final-Recipient: rfc822; kk@cutic.de
Original-Recipient: rfc822;kk@cutic.de
Action: failed
Status: 5.0.0
Remote-MTA: dns; mx01.schlund.de
Diagnostic-Code: smtp; 550-Requested action not taken: mailbox unavailable 550
    invalid DNS MX or A/AAAA resource record

我只是在发送到.de域名时收到此退回电子邮件，有人可以指出我如何解决此问题吗？