When users sign up for an account, they have the ability to subscribe to the newsletter. Unfortunately, there is not a way to disable this section in a simple manner. To send mail to newsletter subscribers, you may follow our guide on sending mail in Opencart.
thanks for your quick response - can I see who has signed up for newsletters??
The default OpenCart setup does not allow for you to view the subscriber list all at once. You will need to explore the different modules regarding newsletters to see which one best fits your needs. Some are free and others you need to pay for. I have a link here to the list of extensions sorted by price.