Exchange 2003 unable to open message for delivery event id 4006

My exchange 2003 is having a spordaic problem for one user sending out bulk email.  The message gets hung up in the queue with the error message  Event ID 4006 MSExchange Transport unable to open message for delivery.  All of the local users in our company recieve the message but none of the external teaming partners do.  I can manually clear the queue, he has immediately resent the message and then it sends properly.  This has happened once on a calender invite and once on just a regular message sent out to approximately 70 people.

I have completely verified that this is not a DNS issue.  I have verified the the SMTP driver on the exchange server is running properly.  All other mail is sending properly and we are recieving email fine.  We are running symantec exchange edition on the server with premium antispam filtering enabled.  I doubled checked to ensure that heuristic diagnostic was turned off, which it was.

 I came across and Microsoft KB article  but we are not getting this particular error message in the event logs.  

The user in question is running Outllook 2007.  He has been sending to this particular email list for several months without issue.  The first time it happened was the beginning of last week. I cleared the queue thinking it was just a fluke.  He sent out several bulk emails out yesterday and it happened again where one got hung up in the retry queue.

Error recorded in application event log
Event ID 4006 MSExchangeTransport
Message delivery to the host "<IP address>" failed while delivering to the remote domain  "<domain name>" for the following reason: Unable to open the message for delivery.

I removed the real ip and domain name.  And I can reach the domain names and Ip addresses throught telnet session.

Thanks for any assistance
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jbmos2333Connect With a Mentor Author Commented:
thanks. I did find that article but I didn't think anything applied.  And of course the error hasn't happened again.  I will go ahead do the metabase resolution to hopefully prevent this from happening in the future.
Stacy SpearPresident/Principal ConsultantCommented:
Try this article

This is one error that I hate. Had it at a client and non of the items in the article seemed to fix it immediately. But, after working through the metabase one, it disappeared the next day.
I came across this thread while troubleshooting why calendar updates were getting hung in the outbound queue of an Exchange 2003 SBS server.  "Unable to open message for delivery" was my smoking gun.  The issue started after upgrading a user from Office 2003 to Office 2007...  

If the above fixes do not resolve the issue for you, try reading this thread:

Which leads you to this hotfix:

Which has resolved my issue.  
I just had this issue with one of my users, and as jeremyliteky1 states the solution was found in a Microsoft hotfix located at:
I have installed the hotfix, restarted services, and enabled the hotfix in the registry. Still having the issue. Outlook 2007 user, Exchange Server 2003 on Win2003, remote server running Exchange 2007 (win2008?) and having Outlook 2007 clients. I have one user where when he creates or edits meeting requests (not sure which, or both) and sends them to one specific domain, they get stuck in the queue. Emails work fine, it's just the meetings with an issue.
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