We have a problem sending email to one of our vendors. Everything was working fine until about 3 days ago when all mail going to domain2.com failed.
User1 on 3/22/2011 1:31 PM
You do not have permission to send to this recipient. For assistance, contact your system administrator.
<mail.domain1.com #5.7.1 smtp;550 5.7.1 Unable to relay for User1@domain2.com>
In message tracking, it gets as far as starting outbound transfer of message then generates the NDR.
I have ran smtp diag from the Exchange server and using my address with User1, it completes successfully; both mail from and rcpt are ok.. I have checked several spam sites and our public address is not found in any blacklist database.
I just sent a test email to that user to generate an NDR and had diagnostic logging enabled for Exchange Transport. The only thing I found in the application log that stands out is where the NDR occurred. It shows that error (unable to relay) on rcpt command, but what I don't get is the remote host IP address is not what resolves to either of their mx records. The smtp diag test resolved the mx records correctly, but Exchange shows something different. I'm at wits end on this one.