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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?

Thanks

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The good news is that if someone is getting a "SMTP 550 5.1.1" then they are talking to your SMTP transport server and there isn't a DNS problem.

The flip side is that there isn't quite enough information to determine the issue. We'll need to know about your Receive Connectors (their networks, authentication settings, and permissions) to try and figure why your system is rejecting the the inbound message attempt. Off hand, it looks like there may be an over zealous relay rejection connector or some email filtering appliance/application is detecting that the intended recipient isn't a valid email address. But that is shooting while blindfolded in a blacked out room, really just need more intel to know for sure.

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A 550 error of 5.1.1 indicates that your friends are using the wrong address when trying to reach you. The full text of the error is probably

"550 5.1.1 User unknown"

or something very similar. This is a message from the mail server of the receiving domain telling your senders that the address they're trying to reach doesn't exist. Does this happen to them on new messages or on replies? If this tends to be more of a reply issue, then you should double-check your account settings to make sure that the "E-mail Address" value you've specified for yourself is correct.

If you've specified a "Reply-To" address, check that as well. If the Reply-To has the same value as the account address, don't specify the Reply-To.

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