550 Address "xxx@yyy.com" assumed to be invalid ;

[sayur]

Hope someone have any idea of the error message i got as below..
A mail message was not sent due to a protocol error.

550 Address "xxx@yyy.com" assumed to be invalid -
Impossible to verify
The message that caused this notification was:


To: <aaa@bbb.net>
From: <xxx@yyy.com>
Subject:

It is only happen when I sent to aaa@bbb.net ; sent to others , working fine. Both sender and recipient address is valid.

thanks.

 

[brontosaurus]

do you know what kind of server is on the other side? Some are capable of doing reverse DNS lookups and blocking messages that don't match up...

 

[sayur]

Problem solved. The other side have spam list..and the email address is on that list ... being blocked.