I’m using an Exchange account in Cached Exchange Mode. I know that I’m looking at a local cache then instead of directly at my mailbox on the Exchange server.
How exactly is synchronization occurring and can I tweak it?
Outlook uses 3 timers to optimize Cached Exchange Mode, namely a download timer, an upload timer and a maximum timer to fall back on.
Downloading server changes
When a server side mailbox change occurs (for instance when a new message arrives or an item in a shared folder is updated by a delegate), Outlook is notified by the Exchange server of this change. By default, Outlook will then wait 30 seconds before synchronizing these changes. If there are any other changes occurring at the server level within these 30 seconds, then these changes are downloaded at the same time as well.
Uploading local changes
By default, when you make a change locally, that change is synced to the server after 15 seconds. When you make another change within those 15 seconds, then the timer is reset again. As now you could in theory hold off synchronization indefinitely, there is the maximum timer. This timer is started after the first change that you made and when it reaches 60 seconds, then a synchronization will occur to upload all the changes that you have made thus far, no matter how many seconds are left on the upload timer.
Tweaking the synchronization timers
You can adjust the above timers if needed by modifying the following registry keys;
0000001e (30 seconds)
0000000f (15 seconds)
0000003c (60 seconds)
Note: For more information about how to implement these changes into the registry, see this registry guide.