SMS Security Best Practices for Sri Lankan Businesses: Protect Your Customers & Brand

SMS is the backbone of customer communication for thousands of Sri Lankan businesses. This guide covers the security practices every Sri Lankan business should adopt when using SMS.

1. Secure Your API Keys

Your SMS gateway API key is as sensitive as your bank account password. If compromised, attackers can send messages on your behalf and damage your sender reputation.

Best practices:

Never expose API keys in client-side code or public repositories
Store API keys in environment variables
Rotate keys every 90 days
Use separate keys for development and production

2. OTP Best Practices

OTP Length: Use 6-digit OTPs minimum. 4-digit codes can be brute-forced. Expiry: Set OTP expiry to 2-5 minutes. Rate Limiting: Limit to 3-5 OTP requests per phone number per hour. Block numbers exceeding 10 failed attempts within 15 minutes. Retry: Implement exponential backoff with max 3 attempts.

3. Preventing SMS Phishing (Smishing)

Smishing is on the rise in Sri Lanka. Fraudsters impersonate banks and delivery companies.

How to protect your brand:

Never include links in OTP messages
Use a consistent sender ID
Include brand context in messages
Educate customers: we never ask for your password via SMS
Monitor for impersonation attempts

4. DNC Registry Compliance

Sri Lanka TRCSL enforces Do Not Contact regulations. Non-compliance can result in fines.

Only send promotional SMS to opted-in users
Include "Reply STOP" in every promotional message
Scrub against national DNC registry before every campaign
Register all sender IDs with TRCSL-approved operators
Max 4-6 promotional messages per month per customer
Store consent records for minimum 2 years

TXTMSG handles DNC scrubbing automatically on every campaign.

5. Data Privacy

Sri Lanka Personal Data Protection Act No. 9 of 2022 requires:

Explicit customer consent (active opt-in)
Purpose limitation for collected data
Data minimisation
Customer access and deletion rights
Breach notification within 72 hours

6. Monitor for Unusual Activity

Watch for: sudden volume spikes, high failure rates, unusual send times, and unknown sender IDs. TXTMSG provides real-time delivery reports.

7. Secure Webhooks

Use webhook secrets or HMAC signatures
IP allowlisting where possible
Validate incoming payload schemas
HTTPS only

Quick Security Checklist

API keys stored in env variables
Keys rotated every 90 days
6-digit OTPs with 2-5 min expiry
Rate limiting enabled
DNC scrubbing active
Opt-out in all promotional SMS
Consent records stored
Webhooks use HTTPS + verification

How TXTMSG Helps

Encrypted API communication (TLS 1.2+)
Automatic DNC scrubbing
Smart Blacklist filtering
Real-time monitoring dashboard
Sender ID protection
24/7 security support

Published July 21, 2026 | TXTMSG Security Team

TXTMSG Security Team

Contributor

Part of the TXTMSG team — dedicated to building reliable messaging infrastructure for businesses across Sri Lanka and beyond.