To find the size of your mailbox, follow these steps;
1. With Outlook open, click your account.
2. Click Folder on the top menu.
3. Click on Folder Properties.
4. Click Folder Size at the bottom of the pane.
5. You’ll see that the size for the mailbox and each subfolder is indicated in kilobytes (KB).
To find the email file (*.ost) location, right click on your email account and select Open File Location.
You will see *.ost file located in C:\Users\username\AppData\Local\Microsoft\Outlook
