Transactional SMS is sent to a customer within 30 minutes of something they did, such as an OTP or a payment confirmation. Service SMS gives existing customers information about a product or service they already use. Promotional SMS advertises. The category decides your template, your consent needs and whether DND blocks the message, so choose it by content, not by what you wish to send.
By Rohit Jadhav. Last reviewed 25 October 2026. This is operational guidance, not legal advice. Classification of a particular message is decided under the regulation and by the operator, so ask your provider if you are unsure.
"Can we send this as a transactional SMS?" is probably the most common question we hear after "how much does DLT cost". People ask because transactional messages are easier to get through, so there is a pull to describe everything as transactional. It does not work, because operators check the content against the category. This guide explains transactional vs promotional SMS, the service category in between, and how to choose. It is part of our main guide to DLT registration in India. For help with templates, Nexcomm's bulk SMS service includes template submission. More guides sit under Compliance & Regulations.
What do the three categories mean?
TRAI's regulation defines them. These are paraphrases of its definitions.
- Transactional message: sent by a sender to its customer in response to a customer-initiated transaction, within thirty minutes of the transaction. Examples in the regulation include OTPs, transaction alerts and confirmations, balance alerts after a completed transaction and refund information. It is not promotional and needs no explicit consent.
- Service message: sent to a customer to provide information about a product or service they use, such as warranty, a product recall, a software upgrade alert, safety or security of the product, periodic balance alerts or information about delivery. It is not promotional. Such messages to the sender's own customers do not need explicit consent. A service message sent to help complete an ongoing transaction does need explicit consent, valid for seven days.
- Promotional message: a message containing promotional material or an advertisement for a product or service. It must carry an opt-out in the same message, and it is delivered only to people who have not blocked that category or who have given consent.
What are service-implicit and service-explicit?
On the DLT portals you pick a template category. Service messages split in two. Service-implicit covers information to your own customers where consent is inferred from the relationship. Service-explicit is for messages that depend on the customer's explicit consent. When you register a template, choose the one that matches the content and how you hold permission. Details on consent are in SMS consent in India.
How do you tell them apart in practice?
| Message | Likely category | Why |
|---|---|---|
| "Your OTP is 482913" | Transactional | Customer-initiated, immediate |
| "Your order has shipped" | Service | Information about a service in use |
| "Your policy renews on 5 Nov" | Service | Information to an existing customer |
| "Flat 20% off this weekend" | Promotional | An advertisement |
| "Your order shipped. Get 10% off your next one" | Promotional | Promotion mixed in |
Treat the table as a guide, not a ruling. The operator reviews the content of each template.
What happens if you mix them?
The regulation says that if promotional content is mixed with a transactional or service message, the whole message is treated as promotional. That is the point most senders miss. An order confirmation that ends with "buy one more and save 10%" is a promotional message, which then needs the promotional category, an opt-out line and delivery rules that respect DND. If you want to promote, send a separate message.
How does the category affect delivery?
Three ways. First, the header suffix: "-P", "-S" or "-T" shows recipients the type. Second, DND rules: a person can block promotional messages, and a promotional message to a blocked number is stopped in DLT scrubbing. Third, templates: each template is registered in one category, and the changing parts must follow the rules in DLT template variables. Headers are covered in SMS sender ID.
A worked example (hypothetical)
An online pharmacy in Pune wants to send four messages. This is an invented example. The OTP at login is transactional. The "your order is on its way" message is service. The refill reminder to a customer who bought the medicine before is service as well, as information about a product in use. The "festive discount on vitamins" message is promotional, with an opt-out line, sent only to customers who have not blocked promotions. When the team tries to add a discount line to the delivery message, the provider warns that it will be classed as promotional, so the line comes out.
Common mistakes in choosing the category
- Calling a promotion transactional. The template is rejected or later flagged.
- Adding offers to service messages. It makes the whole message promotional.
- Sending a transactional message late. The regulation links it to a transaction within thirty minutes.
- Forgetting the opt-out in promotional messages. It is required.
- Using one template for several purposes. Register one template per purpose.
- Ignoring who the customer is. Service messages are for your own customers.
Frequently asked questions
What is the difference between transactional and promotional SMS?
Transactional SMS responds to something the customer just did, within thirty minutes, and is not promotional. Promotional SMS advertises a product or service, must include an opt-out and is not delivered to people who have blocked that category.
Is an order confirmation transactional or service?
It depends on the content and timing. Confirmations of a customer-initiated transaction are listed as transactional. Information about delivery of goods or services is listed as service. Ask your provider how your template will be registered.
Can I add a discount to a transactional SMS?
No. If promotional content is mixed with a transactional or service message, the message is treated as promotional. Send the offer separately.
Do service messages need consent?
Service messages to your own customers about their product or service do not need explicit consent. A service message sent to help complete an ongoing transaction needs explicit consent, valid for seven days.
Which category should I choose for appointment reminders?
Often service, because it is information to an existing customer about a service they use. Confirm with your provider, and keep promotional wording out of it.
Sources checked
All checked on 25 October 2026.
- TRAI, consolidated Telecom Commercial Communications Customer Preference Regulations, 2018 (definitions of transactional, service and promotional messages; header suffixes)
If you are not sure which category your messages fall into and want to talk it through, you can reach our team through the contact page.