Microsoft 365 / Outlook + Mac mail expert for a no-setup desktop capture ap

We're a pre-launch CRM that, with the signed-in user's explicit consent, captures the user's own email and meetings so AI handles their busy work with zero data entry. Our user is a non-technical sales rep who signs up on their own, with no IT support and no admin rights. The goal: they download one thing and it just works, no manual configuration, on both Windows and Mac. The hard problem we want your help on is reaching a self-serve, non-admin user reliably. Standard Graph OAuth often isn't available to this user on its own, so we lean toward a signed desktop agent that reads the mail already synced locally on the user's own machine under their own authenticated session (Outlook on Windows; Outlook or Apple Mail on Mac), with a cloud Graph sync as the fallback wherever it is available. We want the simplest thing that works: ideally one approach, at most one build for Windows and one for Mac. Tell us honestly how close to 100% of self-serve users each approach reaches, and the lightest fallback for the rest. Everything operates within the normal, documented capabilities of the platform and the user's own authenticated session, with the user authorizing the work and staying in full control of their data. Paid consult or a small MVP build, NDA available. Two quick screening questions below.