Distinguish between transactional and non-transactional communication. Transactional = necessary for the provision of services, such as: Confirmation of an appointment Appointment reminder System notifications or security updates → These should always be sent regardless of marketing preferences. Non-transactional (marketing) communication = Newsletters, promotions, customer satisfaction surveys, etc. → These are only sent via the channels for which the customer has explicitly given permission. So the following checkboxes should actually be available in the customer portal or registration form: ☐ Receive confirmations via email ☐ Receive confirmations via text message ☐ Receive reminders via email ☐ Receive reminders via text message ☐ Receive newsletters via email ☐ Receive newsletters via text message → confirmations MUST be checked anyway, but the customer can choose how they are sent (one way or both) → Reminders and marketing should be optional