"Before you hit send on that next email, perhaps you should run down this list, just to be sure:..."
1. Is it going to just one person? (If yes, jump to #10) 2. Since it's going to a group, have I thought about who is on my list? 3. Are they blind copied? 4. Did every person on the list really and truly opt in? Not like sort of, but really ask for it? 5. So that means that if I didn't send it to them, they'd complain about not getting it? 6. See #5. If they wouldn't complain, take them off!
You can find the rest of Seth's email checklist at: http://sethgodin.typepad.com/seths_blog/2008/06/email-checklist.html