Office-js addin must run a task on ingoing email. How?

[Kukulkano]

Hi. We have a COM add-in for Outlook Classic. This examines all ingoing emails for a specific attachment file extension and starts decompression and deycryption automatically upon it received an specific file extention. Now I'm forced to do the add-in in JavaScript with office-js for Outlook New. So far, if the add-in is clicked by the user, I can successfully decrypt the message.

But how to do that automatically? Looks like if my add-in code is not able to run automatically on ingoing emails. I need some sort of onIngoingEmail() event to trigger automatic decryption. How can I solve this? Any hints?