Message reminders are another way to stay on top of your email. When this feature is on, you'll see message reminders at the top of your inbox that remind you to reply to messages you might have missed that are older than 3 days.
The AI-powered notification tool will automatically analyze your inbox to bring those emails to the top that probably need your attention. You will get reminders to reply to messages you may have forgotten about. These notifications will also remind you to send follow-up emails to coworkers they had already emailed and hadn’t heard back in a couple of days.
Microsoft released this feature in July 2021. It will be enabled for all users by default.
At this time, Microsoft has not stated if/when the new capability will be available in desktop versions of Outlook.