How does the app handle email subscription settings?

When someone logs in using a Social network on the website, we will check if they are an existing customer or not. If they are new, we will create their account and opt them into your newsletter subscription by default, i.e. tick the box in their customer profile. 

For any existing customers however, we will not touch their subscription status. 

You may want to reflect this in your T&Cs, that signing up using a social network will by default give their consent to form part of your subscriber list.