I'm having this problem when i'm trying to send an email to this domain and the NDR reply that I get is:
Your message did not reach some or all of the intended recipients. May I know the cause of this error?
Sent: 01/07/2009 11:39 AM
The following recipient(s) could not be reached:
email@example.com on 01/07/2009 11:25 AM
The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
< mail.xxx.com.my #5.0.0 smtp; 550-Callback setup failed while verifying <firstname.lastname@example.org> 550-(result of an earlier callout reused). 550-The initial connection, or a HELO or MAIL FROM:<> command was 550-rejected. Refusing MAIL FROM:<> does not help fight spam, disregards 550-RFC requirements, and stops you from receiving standard bounce 550-messages. This host does not accept mail from domains whose servers 550-refuse bounces. 550 Sender verify failed>