Yes, but this permission or ‘consent’ can either be explicit or implicit. The action of a person subscribing to your list gives you ‘explicit consent’ to send the person emails relating to your products or services. You can also use ‘implied consent’ to send emails to your existing customers. They have implicitly given their consent because they are your customer, and you may email them even if they have not requested to join your mailing list. Whichever type of consent you have, you always need to include the facility in every email for a person to withdraw their consent and unsubscribe from future emails.