發現公司的主機平常時都沒什麼問題，但只要寄給德國的廠商(不同家) 就容易被退信。
是我們的問題還是對方的問題呢?

----- The following addresses had permanent fatal errors ----- <contact@AAA.de>
(reason: 554-kundenserver.de (mxeue106) Nemesis ESMTP Service not available)

----- Transcript of session follows ----- ... while talking to mx00.kundenserver.de.:
<<< 554-kundenserver.de (mxeue006) Nemesis ESMTP Service not available <<< 554-No SMTP service <<< 554-Bad DNS PTR resource record.
<<< 554 For explanation visit http://postmaster.1and1.com/en/error-messages? ip=61.218.226.XXX&c=rdns
... while talking to mx01.kundenserver.de.:
<<< 554-kundenserver.de (mxeue106) Nemesis ESMTP Service not available <<< 554-No SMTP service <<< 554-Bad DNS PTR resource record.
<<< 554 For explanation visit http://postmaster.1and1.com/en/error-messages? ip=61.218.226.XXX&c=rdns
554 5.0.0 Service unavailable