Cannot receive or send emails to one particular customer

[dbar10]

I am running Exchange 2003 on a Server 2003 machine. Recently have discovered that we had one customer that we could not send or receive emails from. I turned up SMTP logging and sent test to the customer and this is the error message that I got:

Event Type: Error
Event Source: SMTP Protocol
Event ID: 7004
User: N/A
Computer: EXCHANGE
Description:

This is an SMTP protocol erro log for virtual server ID 1, connection #288. The remote host "xxx.xx.xxx.xxx", responded to the SMTP command "rcpt" with "550 No such domain at this location (bill@domain.com) ". The full command sent was "RCPT TO:<bill@domain.com ". This will probably cause the connection to fail.

I immediately received an NDR report, it said:

There was a SMTP communication problem with the recipients email server. Please contact your system administrator. <Exchange.ourdomain.com #5.5.0 smtp;550 No such domain at this location (bill@domain.com)>

This is the only recipient taht we are having trouble with but I need to get this straightened out. I suspect that they are running some reverse lookup? How can I fix this on our side?

 

[ntinlin]

Check the MX record that something like MXToolbox.com sees for domain.com.
Then do an NSLookup against your external DNS provider and see what that says.

It could be that they have changed e-mail hosters and the change hasn't got around to your DNS provider yet.
i.e. The server that you are trying to connect to to deliver the mail doesn't actually host their mail domain anymore.

Would also make sense that you can't receive from them if the SPF record for their MX is wrong.

 

[dbar10]

You were right they fixed the problem and all is well. Thanks

 

[ntinlin]

DNS. Dontcha just love it.