I would trust neither of these solution not to have first-party tracking. Outlook might be the exception, but we know MS forces telemetry on its users. A good

I would trust neither of these solution not to have first-party tracking. Outlook might be the exception, but we know MS forces telemetry on its users. A good answer would be to use and SMTP/IMAP client like Thunderbird. Google allegedly stopped reading your mails now... don't know why Gmail is that successful to be honest.