Exchange not sending "acknowledgement"?

Exchange 2003.  I continue to receive the same emails from a few senders.  I do not think the emails are spam.  I receive the duplicates in both Outlook and OWA.  They do not come all together... rather, I receive the duplicates about 30 minutes apart.  It is as if our Exchange server is not sending a message back to the sender's mail server saying "I got it, so you don't have to send it anymore."  Important:  This happens to other users too.

Any thoughts?
K AAsked:
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bsidfwCommented:
Please elaborate, what does "This happens to other users too." mean?   Does that mean that you consistently get repeat messages from multiple different domains?
K AAuthor Commented:
Thanks for your reply... no, I mean other users on this domain... other mailboxes...  Other Outlook users are getting repeated messages too.  That indicates to me that is is (probably) not a virus on my computer, or an incorrect setting in my Outlook, or anything specifically with my mailbox...
K AAuthor Commented:
oh, sorry... the messages are FROM different domains... HP, Southern Living...
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bsidfwCommented:
I would suspect that there might be some corruption in the Exchange Information Store.  ARe you the mail admin or an end user?
K AAuthor Commented:
admin
bsidfwCommented:
How long has it been since you restarted the Information Store?
K AAuthor Commented:
Restarted the whole Exchange Server about Wednesday of last week, but I've planned to do it again during lunch today.... which means about now...  Will do again, and report back to you.
K AAuthor Commented:
Update:  we re-booted our Exchange server, but still continued to get duplicate emails.  Here was our solution:  We're using DynDNS to filter our emails, and we needed to add their IP addresses to our allowed IP Connections in Exchange.  After we did that (though it took about 24 hours to take effect), we stopped receiving the duplicate emails.

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K AAuthor Commented:
We were able to solve this problem ourselves through our own research.
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