SpyPig – Free email Tracking System
http://www.spypig.com/

SpyPig is a free email tracking system that sends you a notification email as soon as the recipient opens and reads your message. SpyPig is dedicated to all those anxious and paranoid individuals out there who can’t stand wondering all day and night if their important email has been read or not. This has been added to Business Intelligence Resources Subject Tracer™ Information Blog. This has been added to the tools section of Research Resources Subject Tracer™ Information Blog.