Can a spam filter work even without reading the content of your messages?
WhatsApp thinks so. Since last April, the messenger app has been successfully fighting spam abuse, even as it’s been using end-to-end encryption.
That encryption means that no one — not even WhatsApp — can read the content of your messages, except for the recipient.
More privacy, however, can raise issues about spam detection. If WhatsApp can’t scan your messages for suspicious content, say for advertisements peddling cheap Viagra, then how can it effectively filter them out?
Source: NW Security 1