When you're using an email program like Outlook its easy to request a read receipt from your recipient so you know when they've gotten your message. With web based email programs like Yahoo! Mail and Gmail however it can be a little harder to know when someone has read your email.

SpyPig is a free email tracking system that is designed to let you know when your friends have read your email, and continues to send an email every time your message is opened by the recipient (up to 5 times). In addition to telling you that your email has been read, SpyPig also tells you the IP address of the recipient. We tested it out on two email addresses on the same computer and SpyPig even let us know we might have opened our own email.

Using SpyPig is as simple giving the site your email address and a title for the email and then selecting your pig of choice to copy and paste into your email message. Using SpyPig requires that both you and your recipient are using HTML-formatted email rather than plan-text or rich-text formatting email so they will download the pig image when they open the email. SpyPig is not recipient specific, so if you send out a mass email then you'll get a notification the first five times the email is opened, but you won't know who specifically opened it.

SpyPig could be great for responding to things like Craigslist ads when you want to know if someone has received your email. SpyPig does pose a bit of a privacy issue. While some of the pigs do indicate they're "spying" others just look like a cartoon pig and don't disclose their spying abilities to the email recipient and either way recipients wouldn't know they were being spied on until they had already read the email.

[via DigitalInspiration]