MailChimp offers a breakdown of what ISPs and receivers are using which types of authentication.

Melissa Read believes managers send surveys too often, causing respondents to burn out on the novelty of providing feedback. Eventually, she said, they’ll stop responding.

One person's valued information may be another person's spam. You know your list is truly opt-in, but people are so sensitive these days that you risk being branded as a spammer even if you believe you've done nothing wrong.