We believe this paper is the first extensive user-study of whitelisting email addresses. While whitelists are common in social networking and instant messaging (e.g., buddylists), they have not caught on in email systems. Instead, most of us use spam filters that try to identify all the senders we do not want to accept email from. With whitelists we only need to identify the much smaller set of users who can legitimately send us email - generally most of these users are known to us. In our study we built and deployed a whitelisting email service - named DOEmail - along with a Thunderbird add-on to try and make whitelists easy to manage. During the past two years, over 120 users have used DOEmail. As expected, we find that almost no spam makes it to users' inboxes, and less than 1% of legitimate email is mis-classified. We measure how hard it is for users to manage their whitelists, and conclude that after initial setup, the burden is very low. Our system uses challenge-responses ...