Pinterest WAU is up 5% but email notification open rates are down 2%. Figure out why.

To diagnose why Pinterest's WAU is up 5% while email open rates have dropped 2%, I would first isolate the factors driving each metric independently. For WAU growth, I'd investigate new user acquisition, feature adoption, and engagement patterns. For declining email open rates, I'd examine changes in email content, send frequency, segmentation, deliverability, and user preferences.

My hypothesis would then explore potential correlations:

1. Cannibalization: Are users engaging more directly with the Pinterest platform (e.g., through push notifications or in-app prompts), reducing their reliance on or interest in email notifications?
2. Content Shift: Has the nature of email notifications changed, making them less compelling or relevant to the user base, even as overall platform engagement increases?
3. Segmentation Issues: Is the WAU growth driven by a demographic or user segment that is less responsive to email, thus diluting the overall open rate?
4. Technical/Deliverability Problems: Are there issues with email deliverability or spam filters impacting open rates, unrelated to user engagement with the platform itself?

I would gather data on user behavior across both channels, A/B test different email strategies, and analyze user feedback to pinpoint the root cause.