End-to-end encryption, which protects message content so that only the sender and recipient can access it, is gaining popularity in messaging applications. At the same time, there is some concern about its deleterious effects on spam detection systems. At WhatsApp we have successfully launched such “e2e” encryption for over 1 billion people – while also reducing the amount of spam they receive. This talk will discuss techniques we’ve found successful for preventing spam without access to message content, and some of the challenges we faced along the way. It should help dispel concerns that e2e encryption necessarily means reduced effectiveness of spam detection.