I have been using outlook at the request of client.  What a pain in the rear-end.  Its like a pretend mail client.  It is like driving an SUV in an Indy race.  Sure, its a larger engine in size and weight, but the body also is heavy, the performance is weak and the thing is going to be
lapped by every car on the track within minutes.  By every car I mean every other client including the web based client I work on for the client that requested I use Outlook, Thunderbird and carrier pigeon.