It's not foolproof and only works when you're sending a message to multiple recipients, but it'll keep you from firing off a rant about your boyfriend to all of your best friends, and accidentally including, say, his mother. Sure, I'd love to have the time to triple-check each and every email, but it's not a realistic option. This lab, and the four that follow, are definite sanity-saving greatest hits.
New Gmail Lab: Got the Wrong Bob? And Four Other Sanity-Saving Labs