Which APIs are the best for my outlook software

Hey community, I want to build a software that would automatically process incoming emails (using an LLM) from an outlook inbox and perform tasks, like forwarding the email to another inbox, or enriching the email body text with data from a CRM.

The software should be easy to integrate into new organisations, so I was looking at building an outlook extensions.But i could not find any triggers that would work on any incoming email. I've looked at the Microsoft documentation for autolaunch add-ins:

https://learn.microsoft.com/en-us/office/dev/add-ins/outlook/autolaunch

But I have seen that I could create a email subscription with the microsoft REST API

https://learn.microsoft.com/en-us/graph/api/subscription-post-subscriptions?view=graph-rest-1.0&tabs=http#request

I also discovered this blog post that revolved around a similar problem

https://techcommunity.microsoft.com/discussions/microsoft-365/trigger-api-from-received-email/3906340 

The suggested solution includes using microsoft power automate, but I would like my solution to work without any additional subscriptions. So my question is, what are the best API's to develop my software. It should be easy to install it on every machine of employees of a client company (like installing the outlook add-on) and analyse the content of the email automatically to then perform some actions, like adding text to the body of an email.

Thanks for any advice in advance :)