From now on, your customers should have full control over what their email is used for.
That's why you have to break up your forms into a few checkboxes for each purpose you want to use the email:
create an account
marketing offers and promotions
Facebook marketing, etc.
Your users should actively give their consent their email to be used for any of these activities. Remember that transactional emails are permitted by default because they're part of the purchase process.
In the example below you see how this shop has two separate checkboxes at checkout:
Metrilo can be integrated with any popup or form so the consent given is recorded into Metrilo's database automatically.