Mail marshal relay error

I was wondering if anyone could point me in the right direction, as I am still new to mail marshal.
I have exchange 2003 running on Server 2003 relaying the mail through the mail marshal.

My e-mails is working 100%, but when I try to send to a specific domain I get the following error almost instantly.

Your message:
   From:    My email account
   Subject: test

Could not be delivered because of

550 <domain email I am sending to>, Recipient unknown

The following recipients were affected:
    Domain email I am sending to



Additional Information
======================
Original Sender:    <my email account>
Sender-MTA:         <my exchange server IP>
Reporting-MTA:      <my mailmarshal server>
MessageName:        <B4a49e38b0000.000000000001.0002.mml>
Last-Attempt-Date:  <12:06:05 Tue, 30 June 2009>

Can anyone please point me in the right direction where to have a look at this?
Is the problem on my mail marshal or on my exchange?
Looking at the error it seems the problem is on my mail marshal but how can I correct this?
hybriddevelopmentAsked:
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Rick FeeMessaging Engineer - Disaster Recovery EngineerCommented:
 The appears to be on the recipient's end with "Recipient unknown"    This could mean the email address does not exist or MM can't connect to the mail server.       From the MM server can you telnet on port 25 to the email server your attempting to send to?     Do you get a banner?      Can you send to this recipient from another test account like yahoo.com or gmail.com?

Run a quick telnet test, example:  Open the cmd prompt.
  1. Type telnet server.com 25
  2. Type HELO server.com
  3. Type MAIL      FROM:you@mydomain.com
  4. You may get a message saying      "250 ok"
  5. Type RCPT      TO:joe@somedomain.com
  6. again, You may get a message      saying "250 ok"
  7. To write the message, type      DATA, followed by your message.
  8. To end the message, put a      period on a new line by itself and press Enter.
  9. Type QUIT to exit      Telnet.
 Let me know what you get and I can help from there...
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hybriddevelopmentAuthor Commented:
The problem I am experiencing is related to my PTR.
It works fin local but when I try to send mail to an international domain it comes back, saying we do not have a PTR.

I have mailed my ISP to sort this out.
Once this is done I will let you know if it works.

Thanks for the help so long.
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hybriddevelopmentAuthor Commented:
Hi Guys

This is working now.
Our ISP made a stuff up with one of our PTR records, this has been sorted and its working 100% now. Thanks for the help
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