Which SMS type should you use? A clear comparison of promotional, service and transactional SMS in India, with timing rules, headers and real examples.
Choosing the wrong SMS type is the most common reason messages get blocked or land with the wrong label. In India, commercial SMS fall into three practical groups: promotional, service and transactional. Here is how they differ.
Promotional SMS
Marketing messages meant to sell: offers, new arrivals, event invitations.
- Header: 6-digit numeric, shown with a -P suffix
- Delivered only in the daytime window set by regulators and operators (commonly from 9 or 10 AM until 9 PM)
- Not delivered to numbers registered on the Do Not Disturb (DND) list for that category
- Example: "Festive sale is live! Flat 20% off till Sunday. Shop: {#var#}"
Service SMS
Messages about a service the customer already uses, such as delivery updates, appointment reminders or renewal notices. Service implicit messages go to existing customers. (Under TRAI's 2025 amendment, service explicit templates are being moved into the promotional category from March 2026, so check with your provider before using them.)
- Header: 6 letters linked to your brand, shown with -S
- Can be sent at any time and reach DND numbers, as long as they contain no promotional content
- Example: "Your appointment at {#var#} is confirmed for {#var#}. Reply C to cancel."
Transactional SMS
Messages triggered by a transaction, mainly OTPs and banking alerts.
- Header: 6 letters, shown with -T
- Delivered 24×7, including to DND numbers
- Example: "{#var#} is your OTP to log in. Valid for 10 minutes. Do not share it."
Quick comparison
| Promotional | Service | Transactional | |
|---|---|---|---|
| Purpose | Sell or promote | Update existing customers | OTP and transaction alerts |
| Header | 6 digits (-P) | 6 letters (-S) | 6 letters (-T) |
| Timing | Daytime window only | Any time | Any time |
| DND numbers | Blocked | Allowed (no promo content) | Allowed |
The one rule that matters most
Never mix promotion into a service or transactional message. "Your order has shipped. Use code SAVE10 on your next order" turns a service message into a promotional one, which can get the template rejected or the message blocked.
Send every type from one account
TextNSMS supports promotional, transactional and OTP SMS on DLT-registered routes, with the right header and template checked before each send. See Bulk SMS or check SMS pricing.
Frequently asked questions
Can I send offers on a transactional route?
No. Any promotional content must go through a promotional template and header. Mixing offers into transactional or service messages can get templates rejected and messages blocked.
Do transactional SMS reach DND numbers?
Yes. Transactional messages such as OTPs and bank alerts are delivered 24×7, including to numbers registered on the DND list.
Related service
Bulk SMS with TextNSMS
Prepaid wallet, pay per message, DLT-compliant routes. Serving Delhi, Noida, Gurgaon and all of India.