You can flag emails for follow-up, and then keep track of them in the Follow Up miniview.

To flag an email for follow-up, select it, and then click the flag icon or the arrow next to it and select an option.




Then you can keep track of the flagged emails in the Follow Up miniview in the bottom left corner of Mail.



If you don't see the Follow Up miniview (if it is the New Notices or To Do miniview instead), you can click the arrow next to the miniview name and then select Follow Up.