In Gmail every built-in view (e.g.: inbox, trash, read mail) is actually a label. So if you want to view all the unread messages from the inbox, you could search for: label:inbox label:unread.
You can combine these built-in labels with your labels and create interesting queries. But these queries can become long and hard to write. Fortunately, you can replace label with l and everything with still work fine. The previous query will become: l:inbox l:unread.
If you still think the query is too long, Gmail has shortcuts for the special labels.
^f sent mail
^t starred messages
^u unread mail
That means our query could become: l:^i l:^u. What about all the unread messages that aren't in the inbox? Search for: -l:^i l:^u.
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