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Ultra-Low Latency Security Infrastructurelow-latency Edge Dispatch

Deliver one-time verification passwords in under 2 seconds guaranteed

When customers wait for an OTP code, every second of latency kills login conversion. Dispatch 2FA and TOTP challenge codes through priority low-latency transactional IP queues.

3,000 emails/month freeZero credit card requiredSub-20ms edge latency
202 Accepted
Ingestion Latency
Queued durably before any provider call
SPF · DKIM · DMARC
Authentication
Aligned on every send
6,000
Free Monthly OTPs
Forever free tier
Developer Ergonomics

Drop into your application in under 60 seconds

Native typed interfaces with zero unnecessary dependencies. Built for standard fetch and modern edge runtimes.

$npm install sadasend
send-otp.ts
typescript
TYPESCRIPT
import { SadaSend } from 'sadasend';

const sadasend = new SadaSend(process.env.SADASEND_API_KEY!);

export async function dispatchLoginOtp(userEmail: string, otpCode: string) {
  return await sadasend.emails.send({
    from: 'security@yourdomain.com',
    to: userEmail,
    subject: `Your Verification Code: ${otpCode}`,
    html: `
      <div style="font-family: sans-serif; text-align: center; padding: 24px;">
        <h2>Your 6-Digit Verification Code</h2>
        <div style="font-size: 32px; font-weight: 700; letter-spacing: 6px; color: #10b981; margin: 20px 0;">
          ${otpCode}
        </div>
        <p style="color: #64748b; font-size: 14px;">Valid for 5 minutes. Do not share this code.</p>
      </div>
    `,
    tags: ['auth-otp', '2fa-challenge'],
    headers: { 'X-Priority': '1', 'Precedence': 'bulk' }
  });
}
Core Infrastructure

Engineered for high deliverability and zero incident risk

Every layer from edge connection pooling to per-key rate limits is designed to keep critical transactional dispatches fast, reliable, and contained.

Priority Edge Queues

OTP and 2FA dispatches are routed through isolated priority delivery queues, bypassing bulk marketing traffic and avoiding delivery lags.

Anti-Prefetch Headers

Security headers prevent enterprise email security scanners (e.g. Mimecast, Proofpoint) from invalidating single-use OTP tokens before users see them.

Real-Time Delivery Confirmation

Synchronous API response returns in under 20ms with message UUID, allowing your auth UI to confirm dispatch to the user immediately.

Domain Reputation Protection

High reputation IP pools and aligned DKIM signatures guarantee primary inbox placement in Gmail, Outlook, Apple Mail, and Yahoo.

Architectural Comparison

SadaSend vs Shared Marketing Senders

Sending OTP codes via marketing email providers puts security codes in the spam or promotional tab. SadaSend uses dedicated transactional IP routes.

Feature & CapabilitySadaSendShared Marketing Senders
Average Inbox Delivery Speed< 2 seconds15 - 90 seconds (Queue delay)
Dedicated Transactional IPs
Anti-Scanner Defense Headers
low-latency Synchronous API
Forever Free Tier
Transparent Economics

Start with 3,000 emails every month at zero cost

No artificial paywalls on security. Unlike legacy providers that reserve recipient allowlists or dedicated IP pools for high enterprise tiers, every SadaSend account receives full safety controls from day one.

3,000 dispatches monthly forever with zero credit card
All safety gates, allowlists, and velocity limits included
Scale seamlessly: Starter ($12/mo for 10k), Pro ($19/mo for 50k), Scale ($79/mo for 250k)
Free Developer Plan
$0 / mo

No credit card required

Create Free AccountCompare all paid plan tiers
Frequently Asked Questions

Everything you need to know about OTP email API

Clear, transparent answers on deliverability, API authentication, and rate limits.

Providers that mix marketing newsletters with transactional emails place security codes in slow, bulk-rate queues behind millions of promotional messages. SadaSend segregates OTPs into sub-second priority queues.
Technical Deep Dives

Related developer guides and architectural tutorials

Explore step-by-step production implementation blueprints, benchmarks, and protocols.

Documentation

REST API Reference & Endpoints

Complete REST API reference for sending emails, managing API keys, tracking delivery events, and configuring recipient allowlists with low latency.

Read guide
Documentation

Official Client SDKs (TypeScript & Python)

Official zero-dependency client SDKs for SadaSend. TypeScript and Python packages are live on npm and PyPI with typed results and auto-idempotency.

Read guide
Documentation

API Error Codes & Troubleshooting

HTTP status codes, machine-readable error reasons, and step-by-step remediation guides for API key rate limits, circuit breakers, and bounce handling.

Read guide
Deep Dive2 min read

Email Threat Modeling for SaaS: Preventing Compromised API Key Abuse

What happens when an engineer accidentally commits an email API key to a public GitHub repo? Here is the threat model and defense blueprint.

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Deep Dive3 min read

Why your transactional email goes to spam

People assume transactional mail is exempt from filtering because it was requested. Mailbox providers do not know that, and mostly do not care.

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Deep Dive4 min read

SPF, DKIM and DMARC: what each one actually does

Three records, endlessly confused with each other. Here is the mental model that makes them stop being confusing, and the two mistakes that cause most failures.

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Deep Dive4 min read

Building a transactional email queue on Bun and BullMQ without losing messages

The worst bug an email service can have is not a crash. It is accepting a message, returning 202, and never sending it.

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Deep Dive3 min read

Nodemailer vs Native Fetch in 2026: Why Modern Runtimes Abandoned Legacy SMTP

Nodemailer served the Node.js ecosystem for 15 years. Here is why modern serverless and edge runtimes have replaced raw SMTP libraries with native fetch.

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