What stresses you is that Outlook will only show you, at a glance, how many new and unread messages have, not the total number. Fortunately, this is but Outlook's default — and can be changed. Note, though, that you cannot have both. Outlook will either show the count of all messages in a folder or the number of unread messages.
See Total (Not Just Unread) Inbox Message Count in Outlook
To have Outlook show you the total number of messages in any folder, say your Inbox, instead of just counting the unread emails:
- Open the desired folder, for example your Inbox, in Outlook.
- Select File | Folder | Properties for "folder name" from the menu.
- You can also click on the desired folder with the right mouse button and select Properties from the context menu.
- Go to the General tab.
- Make sure Show total number of items is selected.
- Click OK.