God, that's been there for days. What are you playing at? Go reply to it.
Got an hour? watch the Inbox Zero video. Inbox Zero is the idea that you 1. stop checking email all the time & check it once or twice a day only, and 2. you look at each email once and then do something with it – delete it, archive it, copy details out of it, forward it, or reply to it. Seriously, watch the video. It'll explain it all.