Mailosaur Alternative in 2026: Why Developers Are Switching to FreeCustom.Email

Introduction

Mailosaur has been a staple of QA teams for years — clean API, solid SDK support, good Cypress integration. But in 2026, development teams are running dozens of parallel CI/CD pipelines, AI agents need programmatic email access, and OTP extraction has become a first-class requirement rather than a nice-to-have.

The complaints about Mailosaur are consistent: there is no free plan, pricing jumps sharply at scale (per-server AND per-user), message retention is just 3 days on Starter, there is no WebSocket push or long-poll endpoint, and OTP extraction is entirely on you — the API returns the raw email body and you write the regex.

This guide gives you a complete, honest comparison of Mailosaur vs FreeCustom.Email, including real SDK code you can copy directly into your test suite.

Mailosaur Pricing (2026)

No free plan. No OTP extraction on any tier. No real-time push. Costs compound with team size.

FreeCustom.Email: The Modern Mailosaur Replacement

FreeCustom.Email is purpose-built for auth flow testing — OTPs, magic links, signup verification, password resets. Every feature exists specifically to make that category of testing faster and more reliable.

Pricing

Installation

JavaScript / TypeScript (Node.js 18+, Deno, Bun)

npm install freecustom-email
# or pnpm add freecustom-email
# or yarn add freecustom-email

Python (3.9+)

pip install freecustom-email

CLI

npm install -g fcemail
# or: brew install fce

SDK Quick Start

JavaScript / TypeScript

import { FreecustomEmailClient } from 'freecustom-email';

const client = new FreecustomEmailClient({
  apiKey: process.env.FCE_API_KEY!, // fce_...
  timeout: 10_000,
  retry: { attempts: 2, initialDelayMs: 500 },
});

// 1. Register a disposable inbox
await client.inboxes.register('test@ditapi.info');

// 2. (trigger your app to send a verification email here)

// 3. Wait for OTP — polls until it arrives (Growth plan+)
const otp = await client.otp.waitFor('test@ditapi.info', {
  timeoutMs: 30_000,
  pollIntervalMs: 2_000,
});
console.log('OTP:', otp); // '847291'

// 4. Clean up
await client.inboxes.unregister('test@ditapi.info');

Python (async)

import asyncio, os
from freecustom_email import FreeCustomEmail

client = FreeCustomEmail(api_key=os.environ["FCE_API_KEY"])

async def main():
    await client.inboxes.register("test@ditapi.info")

    # (trigger your app to send the verification email)

    otp = await client.otp.wait_for("test@ditapi.info", timeout_ms=30_000)
    print(f"OTP: {otp}")  # '847291'

    await client.inboxes.unregister("test@ditapi.info")

asyncio.run(main())

Python (sync — no asyncio)

from freecustom_email import FreeCustomEmail

client = FreeCustomEmail(api_key="fce_...", sync=True)

client.inboxes.register("test@ditapi.info")
otp = client.otp.wait_for("test@ditapi.info", timeout_ms=30_000)
print(f"OTP: {otp}")
client.inboxes.unregister("test@ditapi.info")

Full Verification Flow (Register → Trigger → Wait → Cleanup)

The getOtpForInbox / get_otp_for_inbox helper handles the entire lifecycle in a single call — the recommended pattern for test suites:

JavaScript

typescript

import { FreecustomEmailClient } from 'freecustom-email';

const client = new FreecustomEmailClient({
  apiKey: process.env.FCE_API_KEY!,
});

const otp = await client.getOtpForInbox(
  'mytest@ditapi.info',
  async () => {
    // This callback triggers your app to send the email
    await fetch('https://yourapp.com/api/send-verification', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ email: 'mytest@ditapi.info' }),
    });
  },
  {
    timeoutMs: 30_000,
    autoUnregister: true, // Cleans up inbox after extraction
  },
);

console.log('Verified with OTP:', otp);

Python

python

import asyncio, os, httpx
from freecustom_email import FreeCustomEmail

client = FreeCustomEmail(api_key=os.environ["FCE_API_KEY"])

async def trigger():
    async with httpx.AsyncClient() as http:
        await http.post(
            "https://yourapp.com/api/send-verification",
            json={"email": "mytest@ditapi.info"},
        )

async def main():
    otp = await client.get_otp_for_inbox(
        inbox="mytest@ditapi.info",
        trigger_fn=trigger,
        timeout_ms=30_000,
        auto_unregister=True,
    )
    print(f"Verified with OTP: {otp}")

asyncio.run(main())

WebSocket Real-Time Push (Startup+ plans)

Delivers emails in under 200ms with auto-reconnect — zero polling overhead.

JavaScript

const ws = client.realtime({
  mailbox: 'mytest@ditapi.info', // omit to subscribe to all inboxes
  autoReconnect: true,
  reconnectDelayMs: 3_000,
  maxReconnectAttempts: 10,
  pingIntervalMs: 30_000,
});

ws.on('connected', info => {
  console.log('Plan:', info.plan);
  console.log('Subscribed:', info.subscribed_inboxes);
});

ws.on('email', email => {
  console.log('OTP:', email.otp);            // already extracted (Growth+)
  console.log('Link:', email.verificationLink);
});

ws.on('reconnecting', ({ attempt, maxAttempts }) => {
  console.log(`Reconnecting ${attempt}/${maxAttempts}...`);
});

ws.on('error', err => {
  if (err.upgrade_url) console.log('Upgrade at:', err.upgrade_url);
});

await ws.connect();
// ws.disconnect() when done

Python

ws = client.realtime(
    mailbox="mytest@ditapi.info",
    auto_reconnect=True,
    reconnect_delay=3.0,
    max_reconnect_attempts=10,
    ping_interval=30.0,
)

@ws.on("connected")
async def on_connect(info):
    print(f"Plan: {info.plan}")

@ws.on("email")
async def on_email(email):
    print(f"OTP: {email.otp}")
    print(f"Link: {email.verification_link}")

@ws.on("error")
async def on_error(event):
    if event.upgrade_url:
        print(f"Upgrade at: {event.upgrade_url}")

await ws.connect()
await ws.wait()  # Block until disconnected

See WebSocket documentation.

CLI: Quick Inbox Workflows

# Authenticate once
fce auth login

# Create an inbox
fce inbox create --domain ditapi.info

# Stream emails in real-time to terminal
fce watch mytest@ditapi.info

# Extract the latest OTP — great for shell scripts
OTP=$(fce otp mytest@ditapi.info)
echo "Using OTP: $OTP"

See CLI documentation.

MCP: AI Agent Integration (Growth+ plans)

Mailosaur has no AI-native interface. FreeCustom.Email's MCP server lets Claude, Cursor, and any MCP-compatible AI agent execute complete auth flows with a single tool call.

Configure in Claude Desktop (claude_desktop_config.json):

{
  "mcpServers": {
    "fce-mcp": {
      "command": "npx",
      "args": ["-y", "fce-mcp-server"],
      "env": {
        "FCE_API_KEY": "your_growth_or_enterprise_api_key"
      }
    }
  }
}

Available MCP tools:

Connect via Claude Web:

1. Open Claude Web → Settings → Integrations → Add Custom Connector

2. Set Remote MCP URL: https://mcp.freecustom.email/mcp

3. Set OAuth Client ID: your FCE API key

Error Handling

JavaScript

import {
  FreecustomEmailClient,
  AuthError,
  PlanError,
  RateLimitError,
  NotFoundError,
  TimeoutError,
  FreecustomEmailError,
} from 'freecustom-email';

try {
  const otp = await client.otp.waitFor('test@ditapi.info', { timeoutMs: 30_000 });
} catch (err) {
  if (err instanceof AuthError) {
    console.error('Invalid or revoked API key');
  } else if (err instanceof PlanError) {
    console.error('Plan too low:', err.message);
    if (err.upgradeUrl) window.open(err.upgradeUrl);
  } else if (err instanceof RateLimitError) {
    console.error('Rate limited. Retry after:', err.retryAfter, 'seconds');
  } else if (err instanceof TimeoutError) {
    console.error('No OTP received within timeout');
  } else if (err instanceof FreecustomEmailError) {
    console.error(`[${err.status}] ${err.code}: ${err.message}`);
  }
}

Pytho

from freecustom_email.errors import (
    AuthError, PlanError, RateLimitError, WaitTimeoutError, NotFoundError, FreecustomEmailError
)

try:
    otp = await client.otp.wait_for("test@ditapi.info", timeout_ms=30_000)
except WaitTimeoutError as e:
    print(f"No OTP in {e.timeout_ms}ms for {e.inbox}")
except PlanError as e:
    print(f"Plan too low. Upgrade at: {e.upgrade_url}")
except RateLimitError as e:
    print(f"Rate limited. Retry after {e.retry_after}s")
except AuthError:
    print("Invalid API key")
except FreecustomEmailError as e:
    print(f"[{e.status}] {e.code}: {e}")

See errors documentation.

Full Feature Comparison

FAQ

Q: Does FreeCustom.Email have a free plan? Yes — 5,000 req/mo, 10 inboxes, no credit card. See pricing.

Q: What Node.js version does the SDK require? Node.js 18+. Also supports Deno and Bun. Ships ESM + CJS with full TypeScript types. See JS SDK docs.

Q: Does the Python SDK support sync usage (no asyncio)? Yes — pass sync=True to FreeCustomEmail(). See Python SDK docs.

Q: What is the minimum plan for OTP extraction? Growth ($49/mo). On lower plans the API returns __DETECTED__ as a hint to upgrade.

Q: How does getOtpForInbox differ from calling otp.waitFor manually? getOtpForInbox handles inbox registration, calling your trigger callback, waiting for the OTP, and optional cleanup in one call. It's the recommended pattern for test suites.

Q: Does the SDK retry on network failure? Yes — configure retry.attempts and retry.initialDelayMs in the client constructor for exponential backoff.

Q: Can I use webhooks instead of polling? Yes, on Growth+ plans. The webhook payload includes the pre-extracted otp and verification_link fields. See webhooks docs.

Q: Is there a CLI I can use in CI scripts? Yes — fce otp user@domain.com returns the OTP to stdout, perfect for OTP=$(fce otp ...) shell patterns. See CLI docs.

Conclusion

Mailosaur served the email testing space well, but it lacks the OTP extraction, real-time push, AI-agent support, and free tier that modern development workflows demand. FreeCustom.Email fills every gap — with official SDKs for JavaScript and Python, a CLI, MCP support, and pricing that starts at zero.

→ Get started free → npm install freecustom-email → pip install freecustom-email → Read the Quickstart → Try the API Playground