I point to
and I quote from it.
1. Click on Settings
2. Change Number of messages per page to "no limit"
3. Click on "save" below display tab and Click on "OK" on the pop up
That is the secret my friends
The next time you are in your inbox and Click on the select all rows button (below delete button) and it will select all of the inbox
Click on "delete" button and it is DONE!