Question : Emails failing to be delivered

Hello Experts

I have a client that is trying to receive emails from another company.  The company that is sending the emails are getting NDRs with a diagnostic code of:

SMTP 503; This mail server requires authentication when attempting to send to a non-local e-mail address.  Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.

It sounded like a problem on the sending company's end.  When I did some troubleshooting with their tech support, one of the things I found was that the IP address of the mail server they are sending to is not correct.  There isn't an exchange server on that IP address, although the client's website is on that address.  I thought there might be something wrong with the client's MX records, but after using the MXToolbox to test it all, I couldn't find anything wrong with any DNS related issues concerning their MX records.

At this point, I'm ready to go back to the sending company and have them troubleshoot their mail client, but wanted to ask here first in case there is something else I should try.

Thanks much.

Answer : Emails failing to be delivered

From what you are describing, it definately sounds like a misconfiguration on the sending companys side.  If they are getting authentication errors sending outbound mail, then they have something configured wrong.

Even if they tried to send directly to your client's mail server, they would not get that error as they would be sending to a local mail address at that point.