Operations BroadNet answer

What are SMS OTP best practices?

Last reviewed July 22, 20261 min readReviewed by BroadNet engineering

Quick answer

Deliver SMS one-time passwords over a dedicated high-priority route, keep codes short (4–8 digits), expire them quickly (typically 5–10 minutes), enforce single use, and rate-limit requests per number to defend against SMS-pumping fraud. Put the brand name and the code near the start of the message, include no clickable links (so the message can't be confused with phishing), and configure a fallback channel for when SMS is slow. See /products/otp.

Plain-language definitionVendor-neutralReviewed July 22, 2026

DiagramThe OTP journey, with channel fallback

User requests a codeSign-in, payment or sign-up
Your app calls the verify APIOne request per code
BroadNet delivers the codeOn the best available channelFallback if undeliveredSMSWhatsAppVoice
User enters the codeChecked against the issued code
VerifiedAccess granted

The long answer

Everything worth knowing, nothing that isn't.

§01

Code design and lifetime

Use 4–8 numeric digits — long enough to resist guessing, short enough to type. Set a short expiry (5–10 minutes), invalidate the code after one successful use, and cap verification attempts before forcing a resend. See /answers/what-is-otp and /answers/what-is-2fa.

§02

Defend against SMS pumping (AIT)

Artificially Inflated Traffic — fraudsters triggering floods of OTPs to premium numbers to earn a cut of the traffic — can quietly dominate an OTP bill. Rate-limit per number and per IP, add velocity checks, and monitor sudden spikes to unusual country codes. See /answers/what-is-sms-pumping and /answers/what-is-ait.

§03

Speed and route priority

OTP is time-sensitive: a code that arrives after the user gives up is a failed login. Send OTP over direct, high-priority routes with headroom for bursts, and monitor DLRs so you catch route degradation before users do. See /answers/what-is-dlr.

§04

Add a fallback channel

If SMS is delayed in a market, fall back automatically to flash-call verification, WhatsApp, or voice OTP so conversion doesn't depend on one channel. See /answers/what-is-flash-call-verification and /answers/what-is-silent-network-auth.

§05

Message content and anti-phishing

Lead with your brand and the code, state what it is for, and include no links — legitimate OTP messages never ask the user to click. This trains users to distrust OTP-style messages that do contain links. See /answers/what-is-smishing.

BNWritten by the BroadNet engineering team·Operating carrier-grade messaging since 2003, headquartered in Dubai·Editorial standards

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