Add an e-mail to your Reminders list on OS X to ensure that you remember to reply or complete a task. Here’s how.
Since the Cnet article I linked to appears to be having issues, I’ll tell you that it’s quite simple. Just drag the email from Mail to the Reminders app icon in your Dock. Presto, you now have a reminder titled with the subject line of the email and a link to the email itself in the reminder note.