For us, the one feature that makes or breaks Zimbra in comparison to Outlook is sort by - this is true in webmail and the zimbra desktop:
1. sort by status, especially unread messages. WHY do I have to go to advanced search for this? This is the number one search I do every single day.
2. sort by from- and NOT lose the "from" I currently have selected. The zimbra desktop doesn't allow "sort by from" at all, and the webmail does, but jumps you to the a's. All I want is to select an email address and then sort by that email (yes I know, I can right click and select search - but it is not intuitive nor the way outlook does it).
I really don't want to move to outlook but my staff love the outlook searching. They hate the wildcard searching feature in zimbra.