Webhooks are how email tools talk to everything else. When someone opens an email, clicks a link, bounces, unsubscribes, or completes an automation, a webhook sends that event to your application in real-time. Without webhooks, you're polling APIs, building batch sync jobs, or flying blind.

For developers building SaaS products, webhook quality determines how well your email tool integrates with the rest of your stack. Can you update user records when emails bounce? Can you trigger application logic when someone clicks a specific link? Can you log email events to your analytics pipeline?

I evaluated these based on webhook coverage (what events they expose), reliability (do events actually arrive?), and developer experience (documentation, payload format, retry logic).

What Makes Good Webhook Support?

Event coverage: Delivers, opens, clicks, bounces, spam complaints, unsubscribes, and automation events
Payload quality: Clean JSON with all relevant data (subscriber email, event metadata, timestamps)
Retry logic: Automatic retries if your endpoint is down, with exponential backoff
Signing/verification: Cryptographic signatures to verify webhook authenticity
Documentation: Clear docs with payload examples for every event type
Latency: Events delivered within seconds, not minutes

The 7 Best Options

1. Sequenzy

Best for: SaaS teams wanting email events integrated with product data

Sequenzy's webhook support delivers events for both transactional and marketing email. When emails are sent, delivered, opened, clicked, bounced, or when subscribers unsubscribe, your application receives the event in real-time. This lets you update your product's user records based on email engagement.

For SaaS applications, the practical value is closing the loop. Your app sends events to Sequenzy (user signed up, trial started), Sequenzy sends emails, and webhooks report back what happened with those emails. You can update user profiles, trigger in-app notifications, or log engagement data based on email interactions.

Webhook events: Sent, delivered, opened, clicked, bounced, complained, unsubscribed Pricing: From $29/month Pros: Bidirectional data flow with your app, covers transactional + marketing, clean payloads Cons: Newer platform, fewer webhook event types than Postmark

2. Postmark

Best for: The gold standard for email webhook support

Postmark has the best webhook implementation in the email industry. Every email event is covered: delivery, bounce, spam complaint, open, click, and subscription change. Payloads are clean, well-documented, and include all the data you need. Webhooks fire in near-real-time with automatic retries.

What sets Postmark apart is the inbound webhook. Postmark can receive emails and forward them to your application as webhooks. This enables reply processing, support ticket creation from email, and other inbound use cases. The documentation is excellent, with full payload examples for every event type.

Webhook events: Delivery, bounce, spam complaint, open, click, subscription change, inbound email Pricing: From $15/month Pros: Best webhook implementation, inbound email webhooks, excellent docs, reliable Cons: Focused on transactional email, basic marketing features

3. SendGrid

Best for: High-volume webhook event processing

SendGrid's Event Webhook sends real-time events for every email interaction. The webhook covers delivery events (processed, delivered, dropped, bounced, deferred) and engagement events (opened, clicked, unsubscribed, spam report). Events include categories and unique arguments you set when sending, making it easy to correlate events with your application data.

SendGrid processes billions of emails, and the webhook infrastructure is built for that scale. Events are batched for efficiency (multiple events per HTTP request), which means you need to handle arrays in your webhook endpoint. The documentation includes detailed schemas and test tools.

Webhook events: Processed, delivered, dropped, bounced, deferred, opened, clicked, unsubscribed, spam report, group unsubscribe Pricing: Free for 100 emails/day, from $20/month Pros: Battle-tested at scale, batched events, detailed event types, custom categories Cons: Batched payloads need array handling, marketing features bolted on

4. Resend

Best for: Developers wanting the cleanest webhook DX

Resend's webhook support reflects its developer-first philosophy. Events are delivered as clean JSON with TypeScript-friendly structures. The webhook covers sending events (sent, delivered, bounced, complained) and engagement events (opened, clicked). Setup is simple, and the documentation is excellent.

Resend includes webhook signing for verification, automatic retries with exponential backoff, and a dashboard for monitoring webhook delivery. For developers building in TypeScript, the payload types match the Resend SDK types, making integration seamless.

Webhook events: Sent, delivered, delivery delayed, bounced, complained, opened, clicked Pricing: Free for 100 emails/day, from $20/month Pros: Cleanest DX, TypeScript-friendly payloads, webhook signing, excellent docs Cons: Transactional only, no marketing automation events, newer platform

5. Mailgun

Best for: Developers wanting raw email infrastructure with comprehensive webhooks

Mailgun's webhook system covers every email lifecycle event: accepted, delivered, failed (temporary and permanent), opened, clicked, unsubscribed, complained, and stored (for inbound). Like Postmark, Mailgun supports inbound email processing via webhooks.

Mailgun webhooks include cryptographic signing for security, batch delivery for efficiency, and configurable event types. The events include detailed delivery information like SMTP response codes, which is useful for debugging deliverability issues.

Webhook events: Accepted, delivered, failed (temporary/permanent), opened, clicked, unsubscribed, complained, stored (inbound) Pricing: Free for 100 emails/day, from $15/month Pros: Comprehensive events, inbound webhooks, delivery debugging info, webhook signing Cons: No marketing features, infrastructure-only, documentation could be better

6. Customer.io

Best for: Webhook events from marketing automations and campaigns

Customer.io's webhook support goes beyond email delivery events. You get webhooks for automation events: when someone enters or exits a workflow, when campaigns send, and when messages are delivered or engaged with. This means your application can react to marketing automation state, not just delivery status.

The webhook also supports outbound webhook actions within automations. You can add a "send webhook" step to any Customer.io workflow, calling your application's API at any point in an automation sequence. This turns Customer.io into a programmable automation engine.

Webhook events: Message sent, delivered, opened, clicked, bounced, converted, automation entered/exited, plus custom webhook actions in workflows Pricing: From $100/month Pros: Automation event webhooks, custom webhook actions in workflows, comprehensive Cons: Expensive, complex, overkill for simple webhook needs

7. Amazon SES

Best for: Infrastructure teams wanting raw email events at scale

Amazon SES delivers email events through SNS notifications or Kinesis Firehose. The events cover delivery, bounce, complaint, reject, open, click, and rendering failure. For teams already in the AWS ecosystem, the integration with SNS, SQS, Lambda, and Kinesis provides flexible event processing options.

The downside is complexity. SES doesn't have a simple "point webhook at this URL" setup. You need to configure SNS topics, create subscriptions, and handle SNS message format (which wraps the email event in an SNS envelope). It's powerful but requires AWS knowledge.

Webhook events: Delivery, bounce, complaint, reject, open, click, rendering failure, delivery delay Pricing: $0.10 per 1,000 emails (+ data transfer) Pros: Cheapest at scale, AWS ecosystem integration, SNS/SQS/Lambda/Kinesis options Cons: Complex setup, AWS-specific, no marketing features, raw infrastructure

Webhook Best Practices

Verify Webhook Signatures

Always verify webhook signatures before processing events. Most email platforms sign webhooks with HMAC or similar. Skipping verification means anyone who discovers your webhook URL can send fake events.

Handle Retries Idempotently

Webhooks can be delivered more than once (retries after timeout, network issues). Use event IDs to deduplicate. If you've already processed an event, skip it on retry.

Respond Quickly

Return a 200 status code within 5-10 seconds. If your processing takes longer, accept the webhook, queue the work, and process asynchronously. Slow responses cause retries and can lead to webhook suspension.

Log Everything

Log all incoming webhook payloads for debugging. When an email doesn't deliver or a bounce goes unprocessed, having the raw webhook data is invaluable.

How to Choose

You want the best overall webhook experience: Postmark. The most complete event coverage, cleanest implementation, plus inbound email webhooks.

You're processing high-volume events: SendGrid. Battle-tested at scale with batched delivery.

You're a developer wanting clean DX: Resend. TypeScript-friendly payloads and excellent documentation.

You need webhooks for SaaS lifecycle email: Sequenzy. Bidirectional data flow between your app and email.

You want raw infrastructure webhooks: Mailgun. Comprehensive events including inbound, with signing.

You need automation state webhooks: Customer.io. Webhooks for automation events, not just email delivery.

You want the cheapest at scale: Amazon SES. Pay-per-email with SNS/SQS integration.

FAQ

What's the difference between webhooks and an API? APIs are pull-based (you request data). Webhooks are push-based (the service sends data to you). For email events, webhooks are superior because events happen unpredictably. Polling an API for new events wastes requests and introduces delay.

How do I test webhooks locally? Use a tunneling service like ngrok or Cloudflare Tunnel to expose your local server to the internet. Point the email tool's webhook URL at your tunnel. This lets you receive real webhook events during development.

What if my webhook endpoint goes down? Good email tools retry webhook delivery with exponential backoff (waiting longer between each retry). Most retry for 24-72 hours before giving up. During downtime, events queue on the email platform's side.

Do webhooks affect email delivery speed? No. Webhooks are asynchronous and fire after the email event occurs. They don't block or slow down email delivery. Even if your webhook endpoint is slow or down, emails continue sending normally.