This feature would be crucial for our business, too.
We request and store secondary email addresses during our product onboarding. These manually entered email addresses are much more valuable because our primary addresses are automatically captured upon installing our product.
With Hubspot’s current capabilities, we can only manually target those secondary email addresses with 1-on-1 emails, but with thousands of secondary email addresses, this won’t scale well.
If this feature is going to be in beta, feel free to consider us for testing.