The way I interpret it is that you can email all your free users at the same time, with the below email, but you can't target individuals users and email them one at a time. My guess is what they are trying to avoid is a flow of: user signs up for free account with email => you inbox them saying:

  Subject: save 30% over in-app prices!
  Body:
  "don't pay through the app, use this link to our website"