How to send bulk SMS in India: DLT, sender ID, templates and cost

What is bulk SMS?

Bulk SMS in India means sending the same text message, or a templated message with different details, to many recipients at once, through software instead of by hand. It is the standard way Indian businesses send one-time passwords, order updates, fee reminders, appointment alerts and offers. A gateway sits between your system and the operators and does the sending; you add a contact list and a message. This guide covers the process from registration to your first campaign.

In India the interesting part is not the sending. It is the compliance. The Telecom Regulatory Authority of India (TRAI) requires every business sender to be registered, every sender name to be approved and every message pattern to be approved in advance. Get this right and bulk SMS is fast and cheap. Get it wrong and messages vanish without an error you can see.

How bulk SMS works in India: the DLT framework

To control spam, TRAI introduced the Distributed Ledger Technology platform, universally called DLT. Each operator runs a portal on a shared ledger, and every commercial SMS is checked against it as it passes through the network. Three records matter.

When you send, your provider submits the entity ID, header and template ID alongside the text. The network checks that all three match the registered records and that the text fits the approved template. A mismatch is rejected at the operator, not at your provider, which is why the error is often a bare code. Our DLT registration checklist and the blog post on a DLT checklist for sending SMS in India cover the registration paperwork step by step.

Step by step: sending your first bulk SMS campaign

1. Register as an entity. Use any operator's DLT portal. Keep your PAN, GST or CIN details and an authorisation letter ready. The registration is shared across the networks.
2. Register your headers. Create one header per brand or purpose, for example one for OTPs and one for marketing, and set the category of each.
3. Submit your templates. Write each message once with placeholders for names, amounts and codes. Keep the fixed wording identical to what you will send.
4. Link your DLT account to your provider. Add your entity ID, headers and template IDs inside your SMS provider's dashboard or API settings. We do this for you with Telnxo SMS.
5. Prepare the contact list. Use international format with country code, remove duplicates and landlines, and keep a record of consent.
6. Send a test, then the campaign. Send to a handful of your own numbers on different operators first, check how the text renders, then release the full list.

Sending by API or from a dashboard

For campaigns, a dashboard with a CSV upload is enough. For OTPs, alerts and anything triggered by customer action, call an API. This is what a templated send looks like:

curl -X POST https://api.telnxo.com/v1/messages \
  -H "Authorization: Bearer $TELNXO_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "channel": "sms",
    "to": "+919812345670",
    "sender": "TELNXO",
    "template": "order_update",
    "variables": { "name": "Asha", "order": "4821" }
  }'

The API reference lists every field. If you would rather not code, the same account sends from the dashboard, and you can watch delivery per message under analytics.

Transactional, service and promotional SMS

Operators treat messages differently according to their purpose, and so does TRAI. Pick the right category, because a promotional message sent as transactional is the quickest way to lose a header.

Do not hide offers inside transactional messages. If an OTP message also advertises a product, it is a promotional message and can be blocked. See our guide to opt-outs, sending windows and consent and OTP best practices.

How much does bulk SMS cost in India?

You pay for each segment that is submitted, and the rate depends on the route and your volume. These are the elements that make up your bill.

Use the SMS segment calculator on a draft to see how many segments a message will use, and the cost calculator to estimate a month. The guide to segments and cost explains why one curly quote can double a bill, and the pricing page shows our current rates.

Why bulk SMS gets rejected, and how to fix it

Most delivery problems in India come from a short list of mismatches.

When a message fails, read the status and error code before you guess. Our list of error codes and the article on why messages fail or arrive late help you decide whether it is a content problem, a registration problem or a route problem.

Best practices that improve delivery and replies

• Send from a clear sender ID. A recognisable brand header builds trust and lifts the chance that the message is read. Check formats with the sender ID checker.
• Put the important part first. Phones preview the first line. Lead with what the person needs: the OTP, the amount, the date.
• Keep to one segment. Shorten text and avoid special characters. Use the Unicode checker on text pasted from documents.
• Add a simple opt-out for promotions. A clear way to stop messages protects your sender reputation.
• Segment your list. A short, relevant message to people who asked for it beats a blast to everyone.
• Watch receipts, not just sent counts. Track delivered, failed and rejected, and act on the failed ones the same day.

Many industries have their own patterns: fintech relies on OTPs and payment alerts, education on fee reminders and results, and e-commerce on order updates. See also our marketing and transactional solutions.

Moving from another bulk SMS provider

Your DLT registrations belong to you, not to the provider, so moving is mostly a matter of linking the same entity ID, headers and templates in a new account, running a test and redirecting traffic in stages. Our guides for MSG91 and Textlocal list what to export, what to re-register and how to run both providers side by side for a week.

If you also want to reach customers on chat apps or branded cards, the same account supports WhatsApp and RCS, with SMS as the fallback.

In India, bulk SMS is a registration problem first and a sending problem second.