Boomerang for Outlook
Easy, Integrated Email Reminders for Microsoft Outlook
Boomerang works like a snooze button for your email.
If you get a message that needs your attention at a later time, just select the message, and choose a time from the dropdown. Boomerang will move the message to a storage folder (named Boomerang), and will bring it back to your Inbox at the time you requested.
That way, the message gets your attention when you need it. Boomerang can even return the message flagged for follow up and marked unread.