About 3 weeks ago, we migrated our email solution from one hosted Exchange 2003 environment to another hosted Exchange 2010 environment. I currently have an outside user unable to send emails to our email. Our receive connector has anonymous users allowed and no restrictions and I whitelisted the domain/email for good measure.
When I run a telnet test on that clients SMTP server, I get the error message "550 5.1.1 Recipient Rejected" and through Google, that means it cannot find the user. My guess here is that the end user still somehow has stale DNS records for our email (even though it has been over 3 weeks). How can I verify this other than contacting the provider?