Rules: Do action on the field of referenced node
If your rule is set to React on event: Before saving content or After saving new content of type Article, then do this:

Add condition: Entity has field

ENTITY: node:field-your_reference_field

FIELD: field_email

This makes the referenced node's email field available in to Actions. So then you can

Add action: Send email

To: node:field-your_reference_field:field_email

This should get you where you need to be.