This one is driving me crazy. I'm not sure when this problem started. We have 2 ISPs, Earthlink's T1 service and a local broadband provider. I receive the same error through both ISPs, which leads me to believe it's some type of reverse DNS problem. However, I do have valid Reverse DNS entries setup for both ISPs ... mail.mydomain.com. A reverse DNS lookup on both my IPs resolves correctly.
The error I get is this:
Error: Expected "250". Server rejected the recipient address. Failed to submit mail to mx.mc.surewest.net.
The email address we're trying to send to is another domain, not surewest, so I'm guessing Surewest is their ISP and they host their own server on the Surewest network.
The mail doesn't bounce back and doesn't make it to the recipient. In the past, these emails have bounced back weeks or months later. Our Exchange is set to deliver NDRs if messages are delivered in 3 minutes, so something weird is happening.
I contacted Surewest, and they pretty much told me to call my ISP.
As a test, I just tried an SMTPdiag to yahoo.com domain, and I am also getting a failure:
Error: Expected "220". Server is not accepting connections. Failed to submit mail to c.mx.mail.yahoo.com.
Any help is much appreciated! Thanks.