Instead of converting files first and importing them later, I was hoping to find a tool that could migrate everything directly into an email account.

I found that MacSonik MBOX Converter  supports importing MBOX emails into Gmail, Office 365, iCloud, Hotmail, Yandex Mail, and other email services. It even mentions support for migrating Google Takeout MBOX data directly to Office 365, which sounds useful for anyone moving away from Google services.

I'm curious if anyone here has tried the direct migration feature and how well it worked.