What mail client are you using?
You could initially try running a Windows process to check for any disk file errors, just in case there is any potential file corruption:-
- RIGHT-Click on the 'Windows Start' button, bottom left hand corner of screen and select 'Command Prompt, Run as Administrator'
- Click 'Yes' to the security message prompt
- A blank window will open labeled as 'Administrator: Command Prompt'.
- Within the 'Command prompt' window using the keyboard type the following character text "Chkdsk /F" and then press the keyboard enter key.
- In response to the Windows message "Y/N" question that appears on screen, type "Y" and press the the enter key.
- Now restart the computer and when Windows reboots it will commence a check disk operation and automatically attempt to fix any File disk errors it may find. Let it run which could take some time depending on what it finds.
- When the process is completed Windows will restart automatically where you can then test to see if the problem is fixed.