I'm building a mobile backend and need to send texts at scale

Got it. If you’re building a mobile backend and need to send SMS at scale, the key is to design for deliverability, throughput, cost control, and compliance from the start.

Core approach

1) Use a real SMS provider

Common choices:

• Twilio
• Vonage
• MessageBird
• Plivo
• Sinch
• Regional carriers/aggregators if you need local optimization

Pick based on:

• Countries you need to reach
• Throughput limits
• Cost per message
• Delivery reporting quality
• Support for long codes, short codes, and alphanumeric sender IDs

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2) Build an async sending pipeline

Don’t send SMS directly in your request path.

Typical architecture:

1. Mobile backend receives an event
2. Write message request to a queue
3. Worker service sends via SMS provider
4. Persist provider response + status
5. Handle retries and delivery receipts asynchronously

This helps with:

• Burst traffic
• Provider rate limits
• Retries
• Observability

Use:

• Queue: SQS, RabbitMQ, Kafka, Pub/Sub
• Worker autoscaling
• Idempotency keys to avoid duplicate sends

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3) Separate message types

Treat these differently:

• OTP / verification: low latency, high priority
• Transactional alerts: delivery notifications, status updates
• Marketing/promotional: stricter compliance, opt-out required

For OTPs:

• Short TTL
• One-time token
• Limit resend frequency
• Device/IP throttling

For marketing:

• Explicit opt-in
• STOP/unsubscribe handling
• Quiet hours / regional rules

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4) Plan sender types correctly

Depending on country and use case:

• Long code: standard phone number, lower throughput
• Short code: higher throughput, more expensive, approval needed
• 10DLC (US): required for application-to-person messaging
• Alphanumeric sender ID: common in many countries, not universally supported

For scale:

• Use the sender type that matches local regulations and throughput needs
• Register campaigns where required

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5) Handle compliance

This is critical.

You need to manage:

• User consent / opt-in
• Opt-out / STOP
• Message frequency controls
• Content restrictions by country
• Brand identification and campaign registration

Depending on region, laws may include:

• TCPA (US)
• GDPR / ePrivacy (EU)
• CASL (Canada)
• Local telecom regulations

Keep a consent ledger with:

• Phone number
• Opt-in source
• Timestamp
• IP/user agent if relevant
• Message category consent

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6) Design for retries and failures

Not all failures should be retried.

Classify errors:

• Transient: provider timeout, rate limit, temporary carrier error → retry with backoff
• Permanent: invalid number, blocked, opt-out, unsupported region → stop retrying

Use:

• Exponential backoff
• Dead-letter queue
• Circuit breaker if provider is degraded

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7) Track delivery and performance

Store and monitor:

• Queued
• Sent
• Delivered
• Failed
• Undelivered
• Expired
• Opt-out events

Useful metrics:

• Delivery rate
• Time to deliver
• Cost per delivered message
• Retry rate
• Opt-out rate
• Carrier-specific failure codes

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8) Protect your system from abuse

If SMS is user-facing, attackers may try to:

• Trigger floods
• Abuse OTP endpoints
• Cause cost spikes

Add:

• Per-user rate limits
• Per-phone-number limits
• Per-IP throttling
• CAPTCHA for suspicious activity
• Velocity checks
• Fraud detection rules

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Suggested backend pattern

A robust flow looks like this:

• API receives POST /send-sms
• Validate request and permission
• Create SMS job record
• Push job to queue
• Worker picks job
• Select provider/sender based on destination
• Send SMS
• Persist provider message ID
• Listen for delivery receipts/webhooks
• Update final status

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Example fields to store

For each SMS job:

• id
• user_id
• phone_number
• message_type
• template_id
• body
• sender_id
• provider
• provider_message_id
• status
• error_code
• retry_count
• created_at
• sent_at
• delivered_at

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If you expect very high volume

Consider:

• Multiple providers with failover
• Region-based routing
• Dedicated numbers or short codes
• Message templating and pre-approval
• A service layer just for messaging
• Bulk send optimization
• Daily/hourly sending quotas

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Recommended next step

If you want, I can help you design:

1. a scalable SMS architecture
2. a provider comparison
3. a database schema for SMS jobs
4. a Node.js / Python implementation
5. a cost and throughput strategy

If you tell me:

• expected daily volume
• target countries
• OTP vs marketing vs transactional
• your tech stack

…I can give you a concrete design.