To set emails to automatically decrypt within Outlook, you will need to click on 'File' and then 'Options' to get to your Outlook Options window. From here, click on 'Add-Ins' in the left hand panel.

You will then need to click on the DESlock+ Outlook Add-in listed in the Add-ins window and click the 'Add-in Options...' button which will present you with the following window.

Under the 'Decrypting' heading, you will need to put a tick in the box next to 'Automatically decrypt message text' for emails to automatically be decrypted. You can then choose to either leave the message encrypted or save the message decrypted by selecting the appropriate radio button. You can then click 'OK' to save your changes and close the window.