What does flagging a message mean?

Hello Old School student,

Thank you for posting this case in Microsoft Community!

Based on your description: What does flagging a message mean? I would like to cooperate with you working on this case. To clarify this case, by flagging email messages, you can track responses to messages that you send. You can also make sure that you follow up on messages that you receive. In either case, you can include a reminder alert. Thus flagginga meesage is the basic feature in Outlook but not marked the email as spam. And this make your email messages for follow up and reminder easily.

For more information, you may check this article as reference: Flag email messages for follow up - Microsoft Support.

Hope the above information would be helpful. If you need further assistance, please feel free to let me know, I will keep assisting you.

Your understanding and patience will be appreciated.

Thank you!

It only makes the email Important /Highlights it (kind of like adding a star to it).