So what if you are a Gmail user and you want to know when someone reads your message? It turns out that there is a way to get a read receipt without changing your mail program.
SpyPig is a read receipt service that works with a number of e-mail clients, including Gmail. It's completely Web-based -- there's nothing to install, and you don't have to change the way you use your e-mail software.
The service works by embedding a tracking image in your outgoing message. When the recipient opens your message, SpyPig knows the image has been viewed, and reports back to you with an e-mail confirmation.
The process is somewhat manual. To use SpyPig, you visit the hog-themed Web site, enter your e-mail address, and grab a copy of the SpyPig image. You have several to choose from, including a small pig-face and a less obtrusive blank white square. Paste the image into your e-mail and send it as you normally would.
Of course, no system that games Gmail (and the Internet in general) can be perfect. If your recipient is using a mail client that doesn't automatically download images -- like Outlook, for example -- the recipient will need to manually opt to display images before you get a ping back from SpyPig. If they never choose to display images, you don't get any confirmation.
On the other hand, SpyPig requires no registration, is completely free, and doesn't bother you with advertisements or other annoyances. For those reasons, it's a good tool for those times when you want additional assurance your message is read.