The problem is Microsoft doesn't explain what it's doing. In the settings, the option is Low: Move the most obvious junk mail to the Junk Email folder. What makes it obvious? Our customers (and some of my team) are old-school corporate and institutional people who think emails always go through. False positives shoving real email into Junk would be a problem.

The support page (https://support.microsoft.com/en-us/office/change-the-level-of-protection-in-the-junk-email-filter-e89c12d8-9d61-4320-8c57-d982c8d52f6b) only says: "You can make the filter more aggressive so that it catches more junk messages. The higher you set the protection level, the greater the risk of some legitimate messages being identified as junk." Zero detail.

A blog article at one email marketing company says: "Outlook spam filter evaluates each incoming email to identify potential spam. It looks at things like sent time, trigger words, body content, safe senders list, etc. If it finds enough spam signals from your email, it’ll send the email to the Outlook spam folder." Plausible, but could just be marketing blether to get you to pay them to help your spam avoid spam filters.

I see Outlook.com uses SmartScreen, but desktop Outlook doesn't. Otherwise I can't find any info.

1) Any detailed info on how the desktop Outlook junk filter works? 2) Simplest effective third-party option? 3) Try it and keep an eye on the Junk folder?

Thank you for your input and suggestions.