zoho email was reject by recipient party, some time zoho reject other party's email.

zoho email was reject by recipient party, some time zoho reject other party's email.

hello,

registered zoho mail with my own domain, but , found problem, the zoho email doesn't work well with some specific domain, like qq.com and 126.com,  in some cases, it can go through without problem (sending&receiving), but in many cases, it can't go through, boh sending and receiving.

here is a example of error message(sometimes, the email can went through, sometimes not):


 

This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error.

XXXXXXXXX@qq.com Error, ERROR_CODE :550, ERROR_CODE :Mail content denied. http://service.mail.qq.com/cgi-bin/help?subtype=1&&id=20022&&no=1000726


can you tell me the reason?

thanks?