Usually it's a PST file issue, where the PST folder is at it's maximum 
size if it's a style PST prior to 2k3.  has a 2 gig file size limit.  
OR, the PST file is damaged, and needs to be rebuilt.  Have them run the 
PST Repair tool to rebuild the file.  Have them make sure to allow the 
repair tool to create a backup, just in case.  It's a checkbox on the 
final page where you tell it to repair the file, after it's scanned it 
and determined that there are errors.

--
Glenn Meadows
Mayfield Mastering
2825 Erica Place
Nashville, TN 37204
615-383-3708

On 7/8/2013 1:39 PM, Martin Abell wrote:
> Hello,
>
> Has anyone had a user complain that messages are staying in the Outbox 
> in Outlook after the message is sent?  This is regardless of 
> attachment size (or no attachment) and may be addressed to another 
> user in the same domain on the other side of the office. Attempts to 
> just move the already-delivered message from Outbox to the Sent folder 
> are aborted.  The server logs show everything being delivered.
>
> Martin
> SpeedSpan.
>
>