Recently I'd observed an issue where the outlook would take forever to download new mails and just kept saying "Updating this folder.." in the status bar. I never used to get the emails in time and was getting late in responding because they never arrived :(
I tried several methods but the following is what finally worked for me. Give it a try and see if it works for you too.
File -> Account Settings -> Account Settings -> Data Files (tab) -> <Select the mailbox> -> Settings -> Advanced -> Outliik Data File Settings -> Compact Now
