Bulk SMS service in India: how it works and the rules

Promotional or transactional, DLT templates, sender IDs and what to ask a provider.

Updated 12 October 2026 · 5 min read

How a bulk SMS service works

A bulk SMS service lets a business send one message, or a personalised version of it, to hundreds or thousands of phones at once. You upload numbers from Excel or connect your software through an API, pick a registered sender name and template, and the provider hands the messages to the telecom operators. Each operator then checks the message against your DLT registration and the recipient's DND choice before delivering it.

Three parties have to line up: your business, registered on DLT; the provider, registered as a telemarketer; and the operator. If your registration or template is missing, no provider can deliver your messages through the proper route, whatever its advertising says. The registration itself is covered in our step-by-step DLT guide.

Promotional, service or transactional?

Every bulk SMS falls into one of these, and the type decides who receives it:

Promotional: offers, new stock, an invitation to your stall at a trade fair. It goes out under a numeric sender, is not delivered to people who have blocked promotions, and is sent only during the hours the rules allow.
Service: messages about a relationship that already exists, such as "your order is dispatched", "your payment is due" or "your service visit is tomorrow". It goes out under your lettered sender name.
Transactional: one-time passwords and alerts tied to something the person has just done, such as logging in or paying.

The content decides the type, not your intention. A dispatch message that ends with "Diwali offer: extra discount on your next order" has become promotional. Register it that way, or send two separate messages.

What to ask a bulk SMS provider before you pay

Are you registered as a telemarketer on DLT, and how do you reach the operators? Some connect directly; others resell another company's route.
Do I pay for messages that are not delivered? Some providers charge for every message submitted, including those dropped because of DND or a wrong number. Compare the cost per delivered message, not per credit.
How are credits counted? One credit usually buys one SMS part. In English, a part holds 160 characters, and a longer message is split into parts of 153. Hindi, Marathi, Tamil and other Indian scripts are sent as Unicode, where a part holds only 70 characters (67 when split), so the same message can use two or three times the credits.
Do unused credits expire? Packs often have a validity period. Buy for the next few months, not the next few years.
What reports will I get? Ask for a delivery report per number with the reason for each failure, downloadable to Excel.
Can I schedule, personalise and connect software? Personalisation fills the template's variables from columns in your sheet, such as the shop name or the amount due.
Who helps when messages stop? Template mismatches and unregistered links are the usual causes. A provider that answers the phone saves you a lost day.

Writing a bulk SMS people read

Name your business early. People decide in the first line whether a message is for them.
One message, one point, and one clear next step: call, visit, reply or pay.
Stay within one part where you can. Hindi written in English letters counts as ordinary text, so "Naya stock aa gaya hai" fits more words into a part than the same line in Devanagari.
Match the template exactly, including spaces and punctuation, or the message is blocked.
Avoid writing in capitals or stacking symbols. They look like spam and make people stop reading.

For example, a Surat saree wholesaler writing to retailers who bought last season might send: "Laxmi Sarees, Surat: 40 new georgette designs for Navratri are in. Your area salesman will call this week with rates. Visit us on Ring Road anytime." That is one part, names the sender first, and tells the retailer what happens next.

Where bulk SMS fits for B2B sellers

SMS works best with people who already know you: dealers, distributors, retailers and customers waiting for an update. Dispatch alerts, payment reminders, scheme announcements to your dealer network and meeting reminders get read, because SMS needs no app and no internet connection.

It is weaker for first contact. A promotional SMS from an unknown numeric sender is easy to ignore, and many business owners' numbers are on DND. With new prospects, a short call first, then SMS or WhatsApp to those who agreed, usually works better. If you are building that prospect list, these are the biggest All-India lists in the Starleads catalogue, with the share of contacts that have a mobile number:

Questions people ask

Can I send bulk SMS without DLT registration?

Not through the proper route. Operators block business SMS that do not match a registered sender and template, and sending promotions from ordinary SIM cards can get those numbers disconnected.

Will my promotional SMS reach numbers on DND?

No. Operators filter promotional messages against the DND register before delivery. Our DND guide explains what the register covers and how people use it.

Is SMS or WhatsApp better for B2B?

SMS reaches every phone and suits short alerts. WhatsApp suits catalogues, photos and conversation, but needs the person's opt-in and approved templates; see our guide to WhatsApp marketing for B2B. Many businesses use both.

This is general information, not legal advice. Check the current rules with your provider and on TRAI's website.