On May 25, 2018, the General Data Protection Regulation (GDPR) will come into effect in the EU. GDPR affects all businesses and residents within the EU, so the rules applies even if you your business is outside of the EU (but you sell within it).
If you use Conversio's subscriber lists, you will need to ensure that opt-in confirmation is switched on and customers will need to confirm their email address when they sign up to your lists.
If your previous customers and subscribers did not subscribe in a GDPR-compliant way (i.e. they did not confirm their subscription), you will need to reconfirm their subscription.