Exchange Server unable to receive mail from certain domain

HI,

I have some problem on my exchange server 2003 where a certain domain would get this error when send to our domain recipient.
Error transfering to server; SMTP Protocol Returned a Permanent Error.

When the sender send a mail to 2 of of our domain recipient, mostly only 1 of it would be receiving the mail and the other would receive mail. I have check the exchange system manager and it only prompt one of the recepient email and this apply to the log file as well. The other recipient would not included.

Please help. Thanks