To set emails to automatically decrypt within Outlook, you will need to click on the ESET Endpoint Encryption (EEE) Outlook Add-in listed in the Add-ins ribbon and click the '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. 

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