Occasionally, we receive tickets from users with processes that handle high volumes of email, and they run into an issue where the number of emails they see, via the MS Outlook Email VBO, doesn't match what they see via the Outlook client display.
The vast majority of the time, this issue comes down to the synchronization settings configured between the Outlook client and the Exchange server.
Outlook doesn't typically download and store all messages from the Exchange server, especially for very large/active mailboxes. Instead, Outlook will synchronize with Exchange and keep a subset of those messages in its offline folder. The Outlook API only accesses messages that are contained within the offline folder, so if you're not synchronizing everything, you won't see everything.
There's a good troubleshooting article from Microsoft that discusses this subject and how to change your synchronization settings. You can find it here.
Keep in mind, the more data you download/synchronize, the larger your local .ost file will become and the more drive space you'll consume.
Hopefully this article will help those of you that experience this issue.
Cheers,
Eric
