I put this macOS app together to help me archive a decade of mail from Microsoft Outlook to local storage. (In a format that would outlast an OLM file.) It started as a simple AppleScript script and multiplied by asking myself, "I wonder if I could make it do X..." a hundred times over. The project was ready to share four years ago but a spontaneous cross-country move left it to languish. A recent HN "share your half-baked project" post motivated me to open Xcode and polish it up for 2021. As a former SaaS CTO and Win32 developer in a former life, it was quite a journey down the rabbit hole of macOS app development. Unfortunately, the "New Outlook" doesn't support AppleScript to the extent the "Classic" version does [1], so its shelf-life is unknown. Business/pricing model is TBD. It's free to run in either a limited Trial mode or you can request a beta license key to remove the export message count limit.
[1] https://outlook.uservoice.com/forums/924856-the-new-outlook-...