We are using Outlook 2007 / Vista. Emails are on IMAP. There is a very large file for the inbox and sent mail each are over 5 Gbytes. There are 30,000 emails in the inbox and 17,000 emails in the sent-mail. The user wants it this way. Problem - on startup of Outlook it wants to synchronize the subscribed folders. Takes 10 minutes or more to do this. Then when it's done, it then wants to update the cache when you click the imap inbox or sent-mail. It gets through the sent-mail cache fast, a few seconds for the 17,000 emails. But when you then click on the inbox it starts slowing at 20,000 emails and after minutes it terminates at about 27,000 emails before it gets to 30,000 emails. If you click back and forth between inbox and sent-mail it eventually works itself out and stops updating the cache. But all this time you can't send an email I don't think - it will hang in the outbox. I read the answer about resetting or removing the cache and Microsoft Exchange Server and I also read it on Microsoft but that is for Outlook 2003. I can find no such settings on 2007. Heck, even in the Help on Outlook 2007 they talk about settings that don't exist. They probably didn't bother to update the information.
There is another computer (desktop) also running Outlook 2007 / Vista where we have the same setup going to the same IMAP email account. This desktop has been set up for quite a few months. On it, the synchronization takes only a few seconds. It synchronizes on startup, but also when you hit send/receive. Why would the desktop be so fast for synchronization - seconds - as compared to the laptop - 10 minutes or more - for the same IMAP account? Could it be that the smaller size of the inbox when the desktop was set up allowed it to synchronize all the way, and so each day even with the slightly larger inbox it was ok? But with the new laptop, it sees the huge inbox all at once and has trouble synchronizing - taking 10 minutes. Could it also be that it will just take time -weeks or months - for the laptop cache to catch up with everything and then the laptop will synchronize faster like the desktop? Or perhaps I have a different setting for the laptop as compared to the desktop? I checked couldn't find anything obvious. Both laptop and desktop are bought in the past year and are higher end computers.
New info - sometimes says 'synchronizing hierarchy' and then 'failed to update headers'. Also, I tried using programs scanpst.exe and scanost.exe to correct any errors in the inbox, but when I did a complete search everywhere including system folders it could not find any *.ost or *.pst files.