If you no longer wish your Office 365 account to be connected to the P11D Office 365 OAuth email system follow these quick steps to disconnect your account.
In your browser go to https://myapps.microsoft.com/ and once in there locate the P11D Organiser app. Right click the app icon and select "Manage your Application".
In the subsequent page locate where it says "Revoke Permissions" and click on it. A window dialogue will pop up confirming that you want to revoke permissions from the P11D Organiser application. Simply press the "Revoke" button.
Your Office 365 account has now been disconnected from the P11D Organiser OAuth app. If you wish to connect it back you will have to reinstate the permissions by signing in with your Office 365 account in the P11D Organiser email configuration settings.