Mac Basics: Keeping track of flagged emails
Flagging emails in Mail for later action is all well an good, but it's also easy to lose track of them as they disapear from view. You could always setup a smart mailbox that shows all your flagged mail, but there is a better way that more experienced Mac users do.
In your inbox, sort your mail the way you like it sorted, eg date descending. Now click the Flag column. This puts all your flagged email at the top of your list, but it also retains your preferred sort order.
Now your flagged emails are in your face, never to be forgotten again.