Question about Outlook Express

I am running Mountain Lion, on a top-of-the-line Mac Pro - 64 Gigs of memory, solid state (SSD) hard drive, fastest possible processor. I am connected via Outlook 2011 to an Exchange server. I've noticed that recently, when I search for emails in the "magnifying glass" field at the top right of the window, I get the color pinwheel spinning and a slowdown, as it tries to search. Yes, I have a lot of email, but my machine is very fast and it should not be slowing down like this (and it did not, until recently). I've checked my disk using Disk Utility, I have plenty of free RAM and disk space, and I have rebuilt my identity and rebooted. None of this helped. Any idea what I can do to prevent this slowdown when searching for emails?