Once you open your Inbox, you can quickly distinguish unread threads by their bold font and a small blue circle on the left side of the contact name. But when you have a huge list of threads, it may be difficult to go through all the items to find the unread ones.
'Unread' filter in Inbox
Use the Unread filter to easily access all the threads that have unread messages.
You may also notice the Unread category of messages in the left-side panel of your Inbox, along with the counter of unread messages.
Click on the Unread category in the left-side panel; only threads with unread messages will be shown. This category instantly sorts messages in threads by their unread state, making it easier to work with a huge list of threads. Once you open a thread, it is automatically marked as read, and the counter of unread messages in the left panel will decrease.
By the way, you can always go back to the Inbox to see all the messages.