You built your mobile app with a0.dev because you wanted React Native with Firebase, generated fast. Backed by Y Combinator (W25), a0.dev handles one-click App Store deployment and generates production-ready mobile apps. Now you need email that integrates with your Firebase backend.

a0.dev generates Firebase backends by default, which creates clear integration patterns for email. Firebase Auth handles your users, Firestore holds your data, and Cloud Functions can trigger email when events occur. The best email platform for a0.dev projects should work seamlessly with this stack.

This guide covers 10 email marketing tools that integrate well with a0.dev applications and Firebase. I focused on platforms that work with Firebase Cloud Functions and handle both transactional and marketing needs. If you are building with a different mobile tool, check out our guides for Rork, FlutterFlow, or Draftbit.

Quick Comparison

Tool	Best For	Price at 10k Subs	Firebase Fit	Automation
Sequenzy	SaaS with Stripe	$49/mo	Webhooks	Advanced
Resend	React developers	$20/mo (volume)	Functions	None
Customer.io	Multi-channel	$100+/mo	SDK	Advanced
SendGrid	Firebase native	$20-$90/mo	Extensions	Moderate
Mailgun	Developer control	$35/mo	Functions	Basic
Postmark	Deliverability	$15/mo (volume)	Functions	Basic
Loops	Simplicity	$79/mo	API	Moderate
MagicBell	Notifications	$99/mo	SDK	Moderate
Brevo	Budget + SMS	Free-$25/mo	API	Moderate
Plunk	Open-source	Free-$10/mo	Functions	Basic

1. Sequenzy

Price: Free (100 subscribers) / $49/mo at 10,000 subscribers. Transactional emails included at no extra cost.

a0.dev generates Firebase backends, and Sequenzy's webhook integration syncs Firebase Auth users to your subscriber list. When someone signs up through Firebase Auth, they can automatically enter your welcome sequence without writing custom Cloud Functions.

The platform was purpose-built for SaaS mobile apps, not retrofitted from e-commerce. The visual sequence builder handles onboarding, engagement, and re-activation flows. The AI creates complete email campaigns from a description, matching a0.dev's AI-first approach.

If your a0.dev project uses Stripe for payments, Sequenzy's OAuth integration syncs subscription data automatically. Segment by "trial users" or "Pro plan" without custom code. Revenue attribution shows which emails actually convert.

Sequenzy handles both transactional emails and marketing automation. Password resets from Firebase Auth and your nurture campaigns flow through the same system.

Where it falls short: No push notifications. For mobile engagement, pair with OneSignal or Firebase Cloud Messaging.

Best for: Mobile SaaS founders who want powerful email automation. At $49/mo for 10k subscribers, it beats Loops ($79) and Customer.io ($100+). Small founder friendly with real support.

2. Resend

Price: Free (3,000 emails/month) / $20/mo for 50,000 emails

Resend offers excellent developer experience, and the React ecosystem alignment works well for React Native projects. Call Resend from Firebase Cloud Functions for transactional email.

Where it falls short: No marketing automation. You will need a second tool for sequences.

Best for: Developers wanting clean transactional email with separate marketing.

3. Customer.io

Price: From $100/mo for up to 5,000 profiles

Customer.io handles email, push, SMS, and in-app from one platform. The mobile SDK tracks user behavior in your a0.dev app and triggers multi-channel messaging.

Where it falls short: Expensive. Complex setup.

Best for: Mobile apps with budget for sophisticated multi-channel.

4. SendGrid

Price: Free (100 emails/day) / $20-$90/mo at scale

SendGrid has Firebase Extensions for quick integration. The "Trigger Email" extension sends email when Firestore documents are created. For a0.dev projects wanting minimal configuration, this is convenient.

Where it falls short: Marketing features lag behind. Extension is basic.

Best for: Quick Firebase integration at scale.

5. Mailgun

Price: From $35/mo

Mailgun provides developer-focused infrastructure. Works well with Firebase Cloud Functions. 99.99% uptime SLA.

Where it falls short: Marketing automation is basic.

Best for: Technical teams wanting control.

6. Postmark

Price: From $15/mo for 10,000 emails

Postmark focuses on deliverability. For mobile auth flows where emails must arrive reliably, Postmark excels.

Where it falls short: Basic marketing features.

Best for: Critical transactional reliability.

7. Loops

Price: Free (1,000 contacts) / $79/mo at 10,000 subscribers

Loops offers modern, minimal email marketing. Clean interface, fast setup. Works with Firebase through API calls from Cloud Functions.

Where it falls short: Basic automation. Costs more than Sequenzy.

Best for: Simplicity-focused founders.

8. MagicBell

Price: From $99/mo

MagicBell handles in-app notifications plus email. If your a0.dev app needs a notification center, MagicBell integrates both.

Where it falls short: Email is secondary focus.

Best for: Apps needing in-app notification center.

9. Brevo

Price: Free (300 emails/day) / $25/mo at 20,000 emails

Brevo offers email plus SMS at budget prices. Works with Firebase Cloud Functions.

Where it falls short: Mixed deliverability.

Best for: Budget-conscious apps needing SMS.

10. Plunk

Price: Free (3,000 emails/month) / ~$10/mo for more

Plunk is open-source transactional email. Budget-friendly for bootstrapped a0.dev projects.

Where it falls short: Fewer features.

Best for: Bootstrapped developers.

How to Choose

If you need transactional + marketing

Sequenzy for unified platform. Separate welcome sequences from password resets in one tool.

If you need multi-channel

Customer.io for email, push, SMS together. Or pair Sequenzy (email) with Firebase Cloud Messaging (push).

If budget is tight

Sequenzy's free tier tests full functionality. Plunk for minimal transactional.

Integration Patterns for a0.dev

Firebase Cloud Functions

a0.dev generates Firebase backends. Cloud Functions call email APIs when events occur.

// functions/src/index.ts
import * as functions from 'firebase-functions'
import * as admin from 'firebase-admin'

admin.initializeApp()

export const onUserCreate = functions.auth.user().onCreate(async (user) => {
  await fetch('https://api.sequenzy.com/v1/subscribers', {
    method: 'POST',
    headers: {
      'Authorization': `Bearer ${process.env.SEQUENZY_API_KEY}`,
      'Content-Type': 'application/json',
    },
    body: JSON.stringify({
      email: user.email,
      attributes: { name: user.displayName },
      sequences: ['welcome']
    })
  })
})

Firestore triggers

Cloud Functions can trigger on Firestore document changes. When a subscription document updates, trigger upgrade emails.

Firebase Auth events

User creation, deletion, and password reset events can trigger Cloud Functions that call email APIs.

The Bottom Line

For a0.dev mobile apps, Sequenzy handles email automation excellently with Firebase webhook integration. Pair with Firebase Cloud Messaging for push notifications.

If you want unified multi-channel, Customer.io handles everything together.

For more context, see our SaaS email marketing guide.

Building with a different tool? Check our guides for Rork, Vibe Studio, or FlutterFlow.