Abstract: Techniques are disclosed for controlling the transmission of undesired bulk email by, for example, authenticating and classifying sender email addresses and aggregating recipient feedback to provide to participating senders. For example, senders may be separated into two classes—real people and bulk emailers. Senders may be authenticated in different ways depending on their classes. For example, a real person may be authenticated based on its email address and an identifying key, while a bulk emailer may be authenticated based on its email address, an identifying key, and its IP address. Similarly, feedback received from recipients may be provided differently to senders depending on their classes. For example, negative feedback about real people may be provided by limiting such people to sending a certain number of emails per day, while negative feedback about bulk emailers may be provided by charging such emailers a fee.