I have an older PST file that I keep a lot of my older email in. It’s huge. But it’s well organized and I’m a bit lost without it. I know, I’m an email horde. But, it has "saved" me countless times as I’ve come across something that I’ve discussed or ran across in the past and I can search my PST and find the answer or related discussion. So I started to freak out a little bit (just a little as I have multiple backups of my PST hehe) when I opened my PST in Outlook 2010 (Office 2010 Beta) and in a few of the folders, all I saw was really old messages, even when I knew there were newer messages that should be in there. The messages were there if I opened the same PST in Outlook 2007, so I knew it was either a bug or something else. Come to find out, it was a simple setting that’s hidden pretty well. This lesson shows what I did to see my old messages again.
Where’s My Email Messages?
This screenshot shows a PST folder in Outlook 2010, that should contain a lot of messages from THIS year. As you can tell from the screenshot, all I’m seeing is email from 2006!
How to “See” Again
Turns out that for some reason, certain folders in my PST have a "filter" applied to them. I don’t know why or how, but here’s how to remove the filter. Right click near the top of the window (1) and choose "View Settings" (2).
Dang Filter
Now, click on the "Filter" button. Notice that there is a filter in place since it says "Messages: Advanced" on this screen.
Remove the Filter
Click on the "Advanced" tab (1) and then remove the filter by clicking on the "Remove" button (2). Now click on the "Ok" button (3).
The filter is now off as this screenshot shows. Click on the "Ok" button.
Email Galore!
There you go! All of my email is visiable again.. Whew, glad it’s all still there.. 
THANK YOU! I was ready to KILL Outlook. Now if I could just see how to apply this change to all subfolders, since it affects dozens of folders for me…
Got it: View -> Change View -> Apply Current View to All Folders.
Thanks again!
Thanks! This solved my problem too!