Outlook 2010/Exchange Sent messages Disappear, not received

I have one user (Windows 7, Outlook 2010 and MS Exchange Server) that is having random issues with email.  She types and sends messages via Outlook 2010.  Everything seems 'normal'.  But, she later learns that the recipient didn't receive the message.  Furtehr, the message is not in the Sent folder (as are all other items) and is not stuck in the Outbox.  Its as if the message was never created.  Also, not in 'Draft as the user clicked 'send'. User is also set for cache mode and store is local.

All other users on the network are ok, not seeing this issue at all.  I have already had someone remove and reinstall Office 2010 and the SPs.  Still happens.

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AmitIT ArchitectCommented:
Test same from OWA and check the result. If OWA you don't see any issue. Run outlook in safe mode and test again. I suspect OST corruption or plug-in issue.
MeenanMAuthor Commented:
I appreciate the comment, but the issue is random. It will be fine for a few days, then it suddenly happens again.  Using OWA not really an option.

OST corruption.  Interesting thought.  What if I disable to local copy by turning Cache off for a few days?  Would OST corruption prevent a message from being sent?  Should it not be on the mailbox on the server side as all the other messages are?
AmitIT ArchitectCommented:
OST corruption can cause this issue. You turn off cache mode and few days and test it.

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kensandersonDir of ITCommented:
We're having the same problem.  'Disappearing' emails on 2 users.  We've noticed they both have 'archive' pst's linked in.  We've noticed some network latency on the drive that hosts the archive pst's.  Our theory is that Outlook is dropping the messages from the OST if it potentially loses connection with the PST file.  Currently we've disconnected the PST's from these users to see if that clears things up.

We've already built a new profile for one of these users 2 months ago.  That would have downloaded the mailbox again into a new OST.  This minimizes the possibility of a corrupt OST for that user.
Any ideas?
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