Open an elevated command prompt.
These are three useful commands.
Copy and paste the text under the command
description. Of course, substitute your user
name where mine is. And, do this with WinMail
closed.
Repair-
esentutl /p "C:\Users\MICHAEL\AppData\Local\Microsoft\Windows Mail\windowsmail.msmessagestore"
Defragmentation-
esentutl /d "C:\Users\MICHAEL\AppData\Local\Microsoft\Windows Mail\windowsmail.msmessagestore"
Integrity-
esentutl /g "C:\Users\MICHAEL\AppData\Local\Microsoft\Windows Mail\windowsmail.msmessagestore"