If the message tells you it's been checked at snopes.com and proven valid, the opposite is most likely to be the truth.

The best way to spot an Internet rumor is to Google a distinctive phrase from the message, "putting the passage in quotes." Then you can see what type of Websites display that sort of message. And if you see the text is already on a thousand Websites, maybe that's an indication you don't need to send it on to anyone.

-Joe-