Hi , We have Exchange 2003 environment & office 365 for exchange online. Slowy slowly we are moving the users from Exchange 2003 > 2010 > then cloud. We are experience an issue when office 365 user send a mail to exchange 2003 on premises user, for a particular db ( hosted on exchange 2003) , office 365 user getting a ndr message & saying that
"The message reached the recipient email system but delivery was refused. Attempt to resend the message #5.2.1"
When I checked the Server, I found two event Id is generated, 9667 & 1025.
Any one facing the same issue, please suggest.