Transactional vs Promotional SMS in India

Every commercial SMS sent in India falls into one of two broad categories: transactional or promotional. Getting this classification wrong can mean your messages are blocked, delivered at the wrong time, or flagged as non-compliant. For developers building OTP-based verification, understanding this distinction is critical.

This guide breaks down the key differences between transactional and promotional SMS in India, covering sender headers, delivery timing, DLT templates, DND rules, routing paths, and costs.

Why Categories Matter

India's telecom infrastructure treats transactional and promotional messages fundamentally differently. They travel through different routing paths, are subject to different regulations, and have different delivery guarantees. If you register an OTP template as promotional instead of transactional, your OTPs will not be delivered to DND-registered numbers and will be blocked outside the 9 AM – 9 PM window. For a login flow, that is a critical failure.

TRAI mandates this categorization through the DLT framework. Every registered header and template is tagged with a category, and telecom operators enforce category-specific rules at the network level. For a full explanation of the DLT system, see our DLT registration guide.

Header Types (AX vs BX)

The most visible difference between transactional and promotional SMS is the sender header — the alphanumeric name that appears as the sender on the recipient's phone.

Transactional Headers

Transactional headers are six-character alphanumeric sender IDs. On DLT portals, they are registered under specific prefixes that vary by operator but are generally understood as "AX" type headers (where the exact prefix code is assigned by the operator). These headers look professional and identifiable, for example: ACMECO, STRMSG, HDFC.

Characteristics:

• Six alphanumeric characters
• Custom to your brand name
• Used for OTPs, alerts, confirmations, and service messages
• Registered on DLT portal with transactional category

Promotional Headers

Promotional messages use numeric sender IDs, typically random-looking numbers. These are sometimes referred to as "BX" type headers. The recipient sees a number like VM-884521 or a similar format rather than a recognizable brand name.

Characteristics:

• Numeric sender ID (not brand-identifiable)
• Used for marketing, offers, promotions
• Registered on DLT portal with promotional category
• Lower trust perception from recipients

Comparison Table

Timing Restrictions

One of the most impactful differences is the delivery timing window:

Transactional: No Restrictions

Transactional messages, including OTPs, can be delivered at any time — 24 hours a day, 7 days a week, including weekends and holidays. This is essential for OTP use cases where users may need to verify their identity at 2 AM or on a Sunday.

Promotional: 9 AM to 9 PM Only

Promotional SMS can only be delivered between 9:00 AM and 9:00 PM IST. Messages submitted outside this window are queued by telecom operators and delivered when the window opens. Some operators discard queued promotional messages after 24 hours.

This restriction exists to protect consumers from receiving marketing messages at inconvenient hours. It is strictly enforced at the network level, so there is no workaround. If your use case requires 24/7 delivery (like OTPs), you must use transactional category.

For the latest on timing rules and other regulatory changes, see our article on TRAI SMS regulations in 2026.

DLT Template Categories

When you register templates on a DLT portal, you must assign each template to a category. The main categories are:

• Transactional — triggered by user action, essential for service. OTPs, order confirmations, payment alerts.
• Promotional — marketing intent. Offers, discounts, product announcements.
• Service Implicit — service messages to existing customers based on an existing relationship. Renewal reminders, account updates.
• Service Explicit — service messages where the customer has given explicit consent. Similar to promotional but with documented consent.

Miscategorizing a template is a common mistake. Registering an OTP as "promotional" means it will be subject to DND blocking and timing restrictions, effectively breaking your login flow for a large percentage of users. For detailed template guidance, read our DLT template approval guide.

Consent Requirements

The consent requirements differ significantly between categories:

Transactional Messages

• Implied consent from the service relationship is sufficient
• For OTPs, the user's action of requesting an OTP constitutes consent
• No separate opt-in form required
• Can be sent to DND numbers (consent overrides DND preference)

Promotional Messages

• Explicit opt-in consent required from the recipient
• Consent must be documented and auditable
• Cannot be sent to DND-registered numbers
• Must include opt-out instructions in every message
• Consent can be revoked by the recipient at any time

Under the DPDP Act, the consent requirements for promotional messages are even more stringent. Read about the intersection of data privacy and OTP in our DPDP Act compliance guide.

DND Implications

India's Do Not Disturb (DND) registry, managed by TRAI, allows consumers to opt out of receiving commercial communications. As of recent data, a significant percentage of Indian mobile numbers are registered on DND.

The DND implications for each category:

• Transactional SMS: delivered to DND numbers. TRAI recognizes that transactional messages are essential for service delivery and exempts them from DND blocking.
• Promotional SMS: blocked for DND numbers. If a recipient is on the DND list, your promotional message will not be delivered. This can result in up to 30–40% of your target audience being unreachable through promotional SMS.
• Service Implicit: delivered to DND numbers for categories the consumer has not specifically blocked. Consumers can selectively block categories (banking, real estate, health, etc.).
• Service Explicit: delivered to DND numbers if documented consent exists.

For OTP delivery, this is a non-issue as long as you categorize correctly. OTPs are transactional and will always be delivered regardless of DND status.

Routing and Delivery

Telecom operators route transactional and promotional messages through different infrastructure:

Transactional Routing

• Priority routing with lower latency
• Higher delivery success rate (typically 95%+ for properly formatted messages)
• Real-time delivery with no queuing (outside of network congestion)
• Direct routing through enterprise SMS gateways

Promotional Routing

• Lower priority routing
• Higher latency, especially during peak hours
• Subject to queuing during off-hours (delivered next morning)
• Lower delivery rates due to DND blocking and timing restrictions
• May be routed through aggregator pools, adding latency

For OTP delivery where speed matters (users are waiting on a login screen), transactional routing is essential. A 5–10 second delivery delay on a promotional route can feel like an eternity to a user trying to log in.

Cost Differences

The cost structure differs between transactional and promotional SMS:

While the per-message cost for transactional SMS is higher, the effective cost is often lower because nearly all messages are delivered. Promotional messages have a lower per-unit cost but DND blocking means you pay for messages that never reach recipients.

Choosing the Right Category

Here is a quick guide to categorizing your messages correctly:

StartMessaging Handles It

If you are building OTP-based verification, you should not have to think about SMS categories, headers, DND lists, or timing windows. That is infrastructure complexity, not product development.

StartMessaging handles all of this for you:

• All OTPs are sent through transactional routes for 24/7 delivery
• DND-registered numbers receive OTPs without issues
• Pre-registered transactional headers and templates via our DLT infrastructure
• Priority routing for fast delivery (typically under 5 seconds)
• No DLT registration, headers, or templates needed from your end

Start sending OTPs at Rs 0.25 per message with zero DLT overhead. Learn about our DLT-free OTP delivery, read the no-DLT integration guide, or check pricing for your volume. Explore the full API documentation to integrate in minutes.

Frequently Asked Questions