SMTP relaying denied

The following recipient(s) cannot be reached: on 12/19/2011 9:56 AM
            The e-mail system was unable to deliver the message, but did not report a specific reason.  Check the address and try again.  If it still fails, contact your system administrator.
            < #5.0.0 smtp; 5.1.0 - Unknown address error 550-'5.7.1 <>... Relaying denied. IP name lookup failed []' (delivery attempts: 0)>

Would the above error message be a IP lookup issue our mail server is having with the recipient server ip address?

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The unknown address error part in the error message would mean that the recipients address is wrong.
The receiving server does not know the user so it denies receving it or relaying it further.

Have the user double check the email address
Adam BrownSr Solutions ArchitectCommented:
Another issue may well be that the receiving side doesn't have their MX records configured correctly. Run nslookup in cmd prompt and then type set type=mx and type in the domain of the email that is being rejected. This will let you figure out what the receiving side has their mail flow set for. If nothing shows up or if there is a misconfiguration this will let you know.

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tarik72Author Commented:
The address look good.

Lookup results:

DNS Lookup Results For: 28625 IN MX 5 28625 IN MX 5 28625 IN MX 5 28625 IN MX 5

DNS Lookup Results For: 28800 IN A - this ip was differnt from the one ( in error message.

tarik72Author Commented:
Plus the error message ip does not resolve to anything as well.
Did you try a telnet to port 25 using ehlo to the destination URL name and/or the IP address?
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