Welcome to the forums,
In the main search bar you can type:
is:unread If you want you can even save that search for easy access later!
(also
is:anywhere is:unread &
is:remote is:unread become handy on v5 with shared folders)
Search Tips - Zimbra :: Wiki
You can set your General Options/Preferences to '
Always show search string' to see the current query in the Search toolbar.
For example, when this option is set, clicking your Inbox folder shows the query string
in:inbox.
If you set the
'Initial mail search' to something besides that, upon login you will be taken to that folder/results first.
There's also an advanced graphical search builder: