PDQ Back writes to tell us about an email Microsoft sent to former customers of MSN Music today. The company said it would be turning off the DRM servers used to authorize playback of music purchased from the now-defunct MSN Music store. "'As of August 31, 2008, we will no longer be able to support the retrieval of license keys for the songs you purchased from MSN Music or the authorization of additional computers,' reads the e-mail. This doesn't just apply to the five different computers that PlaysForSure allows users to authorize, it also applies to operating systems on the same machine (users need to reauthorize a machine after they upgrade from Windows XP to Windows Vista, for example). Once September rolls around, users are committed to whatever five machines they may have authorized — along with whatever OS they are running."