Uh real quick here:

POP3 email messages are downloaded from the email server to your computer and stored on the hard drive. (again basic rule of thumb)

If IMAP is used all your email messages are stored on the server and never removed. In most cases Outlook creates a local cache of messages on your hard drive to speed up the opening of emails, but the originals are not touched. Also, with IMAP (this is the big one!) your sent mail and drafts are uploaded to the server! Because of this, you will see the same incoming and sent messages from any computer as long as your mail program is configured for IMAP

In short the reason you cannot see the email is because it is no longer on the server.

YO MLF or any one else, know how to get it back? Can you export to a server???