A transactional SMS answers something the recipient did. A promotional SMS tries to provoke something they did not ask for. Every other difference follows from that one sentence.
What counts as transactional
A message is transactional when the information in it is necessary for something the user already started:
- order or appointment confirmations;
- OTP codes and security alerts;
- shipping and delivery notifications, with tracking numbers;
- payment confirmations and invoice notices;
- reminders for a previously confirmed appointment.
The simple test: if the message never arrived, would the user be missing information they need? If yes, it is transactional.
What is promotional, even when it does not look it
- discounts, campaigns, voucher codes;
- "we added new products to the store";
- abandoned cart recovery;
- holiday greetings with an offer attached;
- satisfaction surveys used as a pretext for an offer.
An otherwise transactional message that also carries a commercial offer becomes, in full, promotional. You cannot mix "your parcel was delivered" with "20% off your next order" and keep the transactional regime.
Why it matters in practice
Consent. Promotional messages need prior, explicit, provable agreement. Transactional ones rest on the existing contractual relationship.
Opt-out. Commercial communication must offer a simple way to unsubscribe, and the request must be honoured immediately and permanently.
Time of day. Commercial messages sent at night generate complaints regardless of what the law allows.
Routing. Carriers treat traffic differently. Promotional traffic pushed through transactional routes eventually means filtering and blocking — including for your legitimate messages.
How to separate cleanly
Keep two distinct flows in your application, with different API keys, different templates and recipient lists built from different sources. Mark each template when you create it, not when you send.
When in doubt about a message, apply the test: could I send this to someone who explicitly asked for no marketing? If the answer is no, it is promotional.
Sender reputation is built over years and lost in a single campaign.
