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If you currently have version 60 or earlier installed (essentially a version released before 2019, when the program underwent its last major overhaul) you should still be able to view the total number of messages (read and unread) per folder from the main folder view. Older versions of the program are capable of viewing this information, however. So, if you have a folder containing a mix of read and unread messages in it, you will only see how many unread are in there if you have a folder containing entirely read messages then the program will not show any messages being in it - at least not until you click into the folder itself. What's unique is that even in newer versions of the program, you can view the number of unread messages stored in each folder, just not the total number of messages there. Unfortunately, that same research states that recent updates to the program have taken this option away.
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Research shows that previous versions of Thunderbird allowed users to see both the number of messages found in each local folder as well as how much space those messages occupied on the hard drive per folder from the main folder view.
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