Bulk SMS & SMS API
Bulk SMS that delivers — OTPs, alerts and campaigns at scale
Send transactional, OTP and promotional SMS across India on DLT-compliant routes — from our campaign platform or a clean REST API, with a delivery receipt for every message.
DLT-compliant routes · Delivery receipts · INR billing
Routes
Transactional vs promotional vs OTP routes
Bulk SMS isn't one pipe. Each route has different sender rules, consent requirements and delivery behaviour — using the right one is what keeps delivery rates high.
| Transactional | OTP | Promotional | |
|---|---|---|---|
| Typical use | Order updates, alerts, reminders | Login and payment verification codes | Offers, sales, re-engagement |
| Sender ID | Registered DLT header | Registered DLT header | Numeric sender per TRAI rules |
| Consent | Implied by relationship | Implied by the transaction | Explicit opt-in, DND respected |
| Delivery window | 24/7 | 24/7, highest priority | 9 AM – 9 PM (TRAI window) |
What is a bulk SMS service?
A bulk SMS service lets a business send text messages to many recipients at once — from a few hundred delivery alerts a day to millions of campaign messages — through carrier-grade connections rather than a phone. Messages are sent from a registered sender ID, tracked with delivery receipts (DLRs), and billed per message part.
You can send two ways: through the web platform (upload contacts, pick a DLT-approved template, schedule, track) or through the SMS API, which drops sending into your own software — OTPs at signup, alerts on order events, reminders before appointments.
SMS remains the one channel that reaches every mobile handset on earth — no app installs, no internet connection, no operating-system dependency. That's why it's still the backbone for OTPs and critical alerts even in app-first businesses.
SMS API
An SMS API developers actually like
One POST to send, a webhook for delivery receipts. Idempotent requests, sensible errors, and the same shape as our WhatsApp and RCS APIs.
curl -X POST https://api.hostmentor.com/v1/sms \
-H 'Authorization: Bearer $API_KEY' \
-d to='+919800000000' \
-d sender='HSTMTR' \
-d template='otp_login' \
-d vars='{"code":"728194"}'const res = await hostmentor.sms.send({
to: '+919800000000',
sender: 'HSTMTR',
template: 'otp_login',
vars: { code: '728194' },
});$client->sms->send([ 'to' => '+919800000000', 'sender' => 'HSTMTR', 'template' => 'otp_login', 'vars' => ['code' => '728194'], ]);
Message parts
How many characters fit in one SMS?
SMS is billed per message part, and the part size depends on encoding. One emoji switches the whole message to Unicode and more than halves the capacity — worth knowing before you write the template.
Standard SMS (GSM encoding)
160 characters per message
“Your order has shipped. Track it at hstm.co/t/4821” — 51 chars, 1 part
Unicode SMS (emoji / special characters)
70 characters per message
“Your order has shipped 📦 Track: hstm.co/t/4821” — Unicode, 2 parts
Longer messages are split and each part is billed as one SMS. Concatenated (multi-part) messages carry a stitching header, so parts hold 153 GSM / 67 Unicode characters. Our platform shows a live part count as you type.
Platform features
Everything a serious SMS operation needs
The platform features that separate a campaign tool from a toy.
Scheduling & throttling
Send now, schedule for later, or drip at a controlled rate so replies don't swamp your support team.
Personalization
Merge variables per recipient — names, order numbers, amounts — from your upload or API payload.
Two-way & keywords
Receive replies on long codes, run STOP/HELP keywords automatically, and route inbound messages to webhooks.
Link tracking
Branded short links with per-recipient click tracking, so SMS campaigns report like email campaigns.
Real-time DLR webhooks
Delivery receipts stream to your endpoint the moment carriers confirm — no polling, no batch files.
Contacts & segments
Lists, custom fields, deduplication and consent flags managed in the platform or synced via API.
Use cases
Where bulk SMS earns its keep
The highest-volume SMS use cases we see across Indian businesses.
Banking & fintech
UPI transaction alerts, OTPs and balance updates — the messages that must always arrive.
E-commerce & D2C
Order confirmations, shipping updates and COD confirmation flows that cut return rates.
Logistics
Pickup, out-for-delivery and proof-of-delivery notifications for drivers and customers.
Healthcare
Appointment reminders, report-ready alerts and vaccination follow-ups.
Education
Admission updates, fee reminders and exam schedules to students and parents.
Local retail
Festival offers and restock alerts to opted-in walk-in customers.
Compliance
DLT compliance, made easy
TRAI's DLT (Distributed Ledger Technology) registration is mandatory for business SMS in India. Skip it and operators silently drop your messages. We walk you through every step.
Register your entity
One-time principal-entity registration on a DLT portal with your business PAN and GST details.
Approve your headers
Register the sender IDs (headers) your messages come from — like HSTMTR — per route type.
Approve your templates
Each message template is registered with variables marked; operators verify every send against it.
Send with confidence
We map your API calls to approved templates automatically, so nothing gets dropped.
Already DLT-registered? Bring your entity ID, headers and templates — we'll map them in a day.
Simple per-part pricing
SMS is billed per message part in ₹, with GST invoices and volume slabs that reward scale. No platform fee to start.
- Billed per part: 160 GSM / 70 Unicode characters (153/67 when multi-part)
- Separate transactional, OTP and promotional route rates
- Delivery receipts and analytics included on every route
- Volume slabs — the more you send, the less each part costs
FAQ
Bulk SMS questions, answered
Character limits, routes, registration and delivery — the details that decide campaigns.
How many characters can one SMS have?
160 characters with standard GSM encoding, or 70 characters if the message contains Unicode (emoji or special scripts). Longer messages split into parts — 153 GSM / 67 Unicode characters each because of the stitching header — and each part is billed as one SMS.
What is an SMS API?
A web API that lets your software send SMS programmatically — your backend makes an HTTP request, and we handle carrier routing, retries and delivery receipts. It's how OTPs, alerts and reminders get sent automatically at any scale.
What's the difference between transactional and promotional SMS?
Transactional SMS covers operational messages (OTPs, order updates) — it's delivered 24/7, even to DND numbers, from registered headers. Promotional SMS is marketing — it needs explicit opt-in, respects DND, and is delivered in TRAI's 9 AM–9 PM window from numeric senders.
What is DLT registration and do I need it?
Yes — DLT registration is mandatory for any business sending SMS in India. You register your entity, sender headers and message templates once on an operator DLT portal; unregistered traffic is dropped. We guide the whole process and map API calls to approved templates automatically.
How fast are OTP SMS delivered?
OTP routes are the highest-priority SMS class, typically delivering within a few seconds. Every message returns a delivery receipt with a timestamp, so you can measure your real p95 latency rather than trust a brochure number.
Can I schedule and personalize campaigns?
Yes. The platform supports contact lists, merge variables per recipient, scheduled and throttled sends, and link tracking — or drive all of it from the API if you'd rather keep logic in your stack.
Can I send international SMS?
Yes — international routes cover 190+ destination countries with per-country rates, alongside your domestic DLT-registered India traffic. One API handles both; the route is chosen by the destination number.
What sender ID will my messages show?
Transactional and OTP messages show your registered 6-character DLT header (like HSTMTR); promotional messages use operator-assigned numeric senders per TRAI rules. We register your headers as part of onboarding.
Start sending SMS today
Get DLT-ready and live in days, not weeks. Tell us your volumes — we'll send the ₹ rate card the same day.
DLT guidance included · GST invoice