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The Zimbra web interface has a cool search folder feature, just like Thunderbird or Outlook, it allows you to specify search criteria, and then save them as a virtual email folder. Every time you go to this folder, the search you specified is performed, and the results are shown in this folder. For people with huge mailboxes, this is a really good thing!

A simple but really useful one is "unread":

• Log in to the web interface
• Click "Advanced Search"
• Click "Status" on the top (Has a little red flag next to it) 
• Tick "unread"
• Click the save icon at the top, next to advanced search (looks like a floppy disk)
• Give the search a name

You can now use this in the web interface, as well as subscribe to it in your mail application if you need to use that. In thunderbird:

• Right-Click the top level of the email account in the "All Folders" pane, eg bob@example.com
• Click "subscribe..."
• Look for the shared folder you just made, tick it and press "subscribe"
• Press OK 

Outlook is pretty similar:

• Right-click account in folder pane
• Click IMAP Folders...
• Select folders and click subscribe

Have a play with the other search options as well, its a nice way to build up searches