Message Internet headers in Outlook 2010

Am having a problem when trying to view internet message headers in Outlook 2010.  

We are having a problem with message Replies getting lost.   When we send a new message, our clients gets them just fine, however if we reply to one of their messages, they never get the reply.   We have traced some of this back to RBL lists and our Hosting company assures us that they have "rotated their servers" and have none on any blacklists.    Anyway, to help them troubleshoot this, the Hosting company asked us to send the "Full Message Header" text available in the email properties of a message that was "lost".   They really mean, "Internet header" text but anyway, when you go to the "Sent" folder and select a message, double click on it to bring it up in a separate window, Click "File" tab, Click "Properties" button, the Internet header field is blank, like completely empty.   Selecting a message from the Inbox works just fine.   Is it possible to find what the Internet header is on a Sent Message?
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Mohammed KhawajaManager - Infrastructure:  Information TechnologyCommented:
The Internet header can also be seen on the receiving MTAs.  If you would like to know if your email domain is still on the blocked list, go to and perform tests.
Dave BaldwinFixer of ProblemsCommented:
Mail clients don't add the 'internet' part of the headers.  The messages in the Sent folder don't have 'internet' headers because what you see there is before the mail server adds them.

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