How to Assess Who's Going to Get That Icky Feeling

I remember seeing a tweet yesterday where someone got an email from an organization that started with, since you used our services in the past and we've had contact. That's just creepy. But understanding of it actually being relationships is so important. So going back to how you, if you're the one in charge of doing that newsletter or news, email, how do you assess who's going to get that icky feeling? How do you check the validity of the information you're using to reach out and do that?"