Transactional emails and unsubscribe

Emails that are part of a running transaction, like invoices, quotes, booking confirmations, appointment reminders, and payment receipts, are classified as transactional. These messages exist to complete an agreement the customer has already entered into, so an opt-out would not make sense: a customer cannot unsubscribe from their own invoice.

Marketing emails are different. Newsletters, promotional campaigns, and prospect outreach always include an unsubscribe link, because those recipients can choose not to receive them.