Why Event Webhooks Matter for Deliverability Tracking

You send an email campaign. It lands in inboxes. Or it doesn’t. No alert. No reason. Just silence. Then, days later, you learn 14% bounced — too late to fix anything. That’s what happens when you rely on delayed reports instead of real-time event data.

Event webhooks are the lifeline of email deliverability. They deliver delivery, open, click, and bounce events the moment they happen — not hours later in a dashboard. Without them, your send strategy is based on guesswork, not insight.

Amazon SES and SendGrid both offer event webhooks, but their execution isn’t the same. One sends raw, consistent data. The other adds noise, delays, and inconsistent formatting. These differences shape whether your list stays clean, your reputation holds, and your messages actually reach inboxes.

Key takeaways

  • Event webhooks provide real-time, actionable data on delivery, opens, clicks, and bounces — critical for spotting issues before they damage sender reputation.
  • Amazon SES delivers event data with consistent, predictable structure and lower latency, enabling faster list hygiene and automation.
  • SendGrid’s event webhooks include additional metadata but exhibit higher variability in delivery timing and format, increasing complexity for integration and error handling.

How Amazon SES Publishes Events to S3, Lambda, or SNS

You can configure Amazon SES to send delivery event notifications to S3, Lambda, or SNS, but you must set up a destination first. SES publishes these events in JSON format with metadata like message ID, recipient, sending IP, timestamp, and event type (delivered, bounced, opened, clicked). You can use SNS as a relay to trigger Lambda functions for real-time actions like suppressing hard bounces or updating user engagement scores.

Pushing Events via SNS, Lambda, and S3

Amazon SES uses SNS as the default intermediary for event delivery. You create an SNS topic and subscribe it to Lambda, S3, or other endpoints. This setup lets you offload event processing to serverless functions, making it ideal for automated workflows. For example, a Lambda function can immediately flag a bounced email address and remove it from your mailing list.

S3 is useful for long-term event logging and auditing. SES writes event records to S3 in batches, which you can later analyze with tools like AWS Glue or Athena. While convenient for compliance, S3 isn't ideal for real-time tracking since the data appears with a delay.

SNS offers the middle ground: it's nearly real-time and reliable. When you publish an event to SNS, subscribers like Lambda or even third-party apps can react within seconds. This makes SNS the most commonly used destination when you need to act quickly on delivery outcomes. According to AWS documentation, SNS supports push-based messaging to thousands of subscribers with high durability and low latency.

What Events Include and How to Use Them

Each event notification includes event type, timestamp, source IP, message ID, and recipient. For tracked emails, you get delivery, open, click, and bounce events—essential for building engagement models or identifying invalid addresses. The message ID helps correlate events back to your original send.

With proper setup, you can enrich your CRM or email platform. A Lambda function can analyze bounce reasons (e.g., mailbox full vs. invalid) and update sender reputation signals accordingly. This level of automation improves long-term deliverability and reduces list churn.

While SES provides detailed event metadata, it doesn't track engagement beyond what’s sent via URL tracking or pixel-based opens. For a complete picture, you need to pair this with your own tracking methods—or use tools that validate email lists upfront. MailTester’s bulk verification helps catch invalid addresses before you send, reducing bounce risk and improving your send quality. Verify your list in seconds.

How SendGrid Delivers Events via Webhook Endpoints

SendGrid sends real-time delivery events directly to a webhook URL you configure. Each event arrives as a structured JSON payload with consistent fields—event type, email address, timestamp, status, and event-specific details like open IP or click URL—enabling you to track bounces, opens, clicks, and more reliably at scale. This direct integration lets you automate response logic without polling.

Event Payload Structure and Consistency

Every webhook event from SendGrid includes a standardized set of core fields, making integration predictable. The event field identifies the event type (e.g., delivered, bounced, opened), email contains the recipient address, and timestamp logs when it occurred. Status codes appear in status, and additional context like ip for opens or url for clicks comes in the data object. This structure simplifies parsing and reduces errors in downstream systems.

Let’s say you’re tracking hard bounces. You’ll see a event: "bounce" with status: "4xx", and the data.reason field will tell you if it was due to a syntax error or a permanent block. This fidelity helps avoid false positives in your list hygiene workflow. The consistent layout also makes it easier to build shared event listeners across multiple services, like customer support or delivery systems.

Scaling and Delivery Reliability

SendGrid supports up to 100 concurrent webhook deliveries per second. That’s important if you send hundreds of thousands of emails daily—even if you have peaks, the system can handle them without dropping events. If your endpoint is unreachable, SendGrid retries with exponential backoff and can queue up to 48 hours’ worth of events, ensuring you don’t lose critical delivery signals.

This retry mechanism is industry-standard but rarely implemented consistently by all providers. For high-volume senders, dropping 0.1% of events can impact deliverability scoring. By maintaining a reliable delivery queue, SendGrid preserves data integrity across large campaigns.

When testing your own event flow, you can use tools like Mail-Tester to simulate real user engagement and verify your webhook logic handles incoming data correctly. For ongoing list hygiene, ensure only validated addresses are on your list—use the bulk verification tool to weed out invalid or risky emails before deployment.

Event Types: Differences in Reporting Scope and Accuracy

SendGrid delivers richer, more out-of-the-box event data than Amazon SES. While both track delivery, bounces, and clicks, SendGrid includes open tracking by default and reports additional events like spam reports and unsubscribes—critical for compliance and list hygiene. SES requires manual pixel embedding for opens, which delays detection and reduces accuracy. For real-time deliverability monitoring, SendGrid’s broader event scope offers a clearer operational picture.

Open Tracking: Default vs. Manual Implementation

You get open tracking with SendGrid right away—no extra setup. It’s baked into their event webhooks, so every email open sends a real-time event, assuming the client loads images. Amazon SES, though, doesn’t report opens natively. To track them, you must embed a tracking pixel—usually a 1x1 invisible image hosted on your server or via a third-party service. This adds latency and relies on email clients allowing remote content, which many modern clients block by default. As a result, open rates from SES are often estimated, not confirmed.

Even with pixel-based tracking, you’re still limited by image loading behavior. A 2023 report from Email on Acid notes that less than 50% of emails see pixel loads in modern inboxes, particularly on mobile platforms where images are often auto-blocked. Without a reliable, in-system signal, your open data becomes a rough estimate at best. If you need accurate insights into user engagement, this gap matters.

Additional Event Types: Compliance & List Health

SendGrid’s event webhook includes several events that SES cannot report directly. These include spam reports and group unsubscribe events—both essential for maintaining sender reputation and compliance with CAN-SPAM and GDPR. When a user marks your email as spam or unsubscribes from a list, SendGrid sends that update to your webhook in real time. You can then remove the address from your database immediately, avoiding future delivery issues.

SES only reports delivery, bounce, and click events. You must build custom logic to interpret spam reports, which often arrive via feedback loops through ISPs, not through SES itself. Even then, feedback loops are delayed—days or weeks—not real time. The lack of native spam reporting and unsubscribe tracking in SES means you’re relying on reactive measures rather than proactive list hygiene.

For teams using third-party tools, this gap can lead to missed signals. Using a service like MailTester to verify your list before sending—even with tools like SendGrid or SES—can prevent delivery issues at scale. Their bulk verification checks for invalid addresses, catch-alls, and disposable domains, reducing bounces and improving overall deliverability.

Webhook Delivery Reliability and Retry Patterns

SendGrid retries failed event webhooks up to five times over two hours using exponential backoff, making it reliable for time-sensitive deliverability tasks like immediate bounce suppression. Amazon SES leverages SNS with up to three days of automated retries, but failures may require manual scrutiny of dead-letter queues. For real-time tracking, SendGrid’s pattern is more predictable.

SendGrid’s Retry Strategy: Consistent and Time-Bound

SendGrid implements up to five retry attempts over a two-hour window when a webhook fails to reach your endpoint. Each retry uses exponential backoff—starting at 30 seconds and doubling with each try—giving transient network blips a strong chance to resolve. This design is well-suited for actions that need to happen fast, like updating suppression lists upon a bounce. If you're using SendGrid for campaign delivery, these retries reduce the risk of missing critical status updates.

Amazon SES and SNS: Longer Retries, More Oversight

Amazon SES uses SNS as its delivery mechanism, which supports auto-retries for up to 3 days. SNS will keep trying to deliver the event message even after sustained network issues, which is useful if your API is temporarily unreachable. However, if all retries fail, the message goes into a dead-letter queue (DLQ) that you must monitor manually. This adds overhead—especially if you're not actively checking logs or setting up alerts. Without active oversight, delivery failures can go unnoticed for days.

If you're building a system that depends on immediate feedback—like blocking a suspicious email address on a hard bounce—SendGrid’s shorter, more consistent retry window offers a clearer fallback than SES’s longer but less predictable delivery path. That said, SES’s extended retry period is better for non-critical events where delayed processing is acceptable.

For teams managing high-volume email sends, testing your webhook endpoints under load is essential. Use tools like inbox placement testing to simulate real-world delivery conditions and confirm your webhooks are receiving events as expected. You can also validate individual addresses with our real-time verification API or clean large lists through bulk verification.

While both platforms support event delivery, SendGrid’s retry logic is more predictable for time-sensitive actions. SES’s model works well in high-availability setups that include automation for DLQ monitoring, but it’s not passive. A failure in the chain still requires human or script-based intervention to prevent silent drops.

The Real-World Impact on List Hygiene and Sender Reputation

If your email service misses or delays event webhooks—like bounces or complaints—you won’t catch invalid or risky addresses fast enough. This delays list hygiene, raises your bounce rate, and can hurt your sender reputation. ISPs notice consistent hard bounces and react by throttling or suspending delivery, even with a small number of bad addresses.

Delayed Event Processing Costs You Deliverability

Let’s say a malformed email address sends a hard bounce. If your webhook system misses it for just 24 hours, that address stays in your list. Over time, uncleaned bounces accumulate. Even a 5% delay in event detection can add 1.2 to 2.5 percentage points to your hard bounce rate across a 10,000-email campaign. That’s not just a data blip—it’s a direct path to ISP suspicion.

Spamhaus and other reputation systems track aggregate bounce behavior. A single undetected bounce from a malformed address rarely triggers instant failure. But repeated or undetected failures from similar domains or patterns can trigger a temporary delivery suspension. This isn’t theoretical—many senders face these issues after neglecting real-time event tracking.

How Webhook Reliability Affects Sender Trust

Amazon SES and SendGrid both support event webhooks, but their reliability depends on your infrastructure. If your webhook endpoint fails to respond or time out, events can be lost. Unlike a direct list verification, webhooks rely on infrastructure uptime, network stability, and proper parsing. Missing them means you’re relying on post-send audits—too late to prevent reputational damage.

MailTester’s real-time verification API and bulk list checks help reduce this risk before sending. You can verify lists at scale before deployment, catching invalid addresses early. Then, use inbox testing to validate deliverability in real inboxes with actual email clients. That layer of pre-delivery verification gives you a cleaner baseline, making your post-send event tracking more accurate and actionable.

Think of webhooks as your second line of defense. They catch issues you might miss. But if they break or delay, your list hygiene suffers. The longer you wait to act, the harder it is to recover. You’re not just managing bounces—you’re protecting your sender reputation over time.

How MailTester Solves the Pre-Send Problem

You don’t need to wait for webhooks to realize your emails are failing. Before sending, MailTester runs a bulk verification process that identifies invalid, catch-all, disposable, and role-based addresses with 98.9% accuracy. This cuts out bad data upfront, reducing bounces, protecting sender reputation, and improving deliverability before the first message hits the wire.

Pre-Send Verification Reduces Deliverability Risk

Let’s be honest: no webhook can fix a list full of dead or spam trap addresses. The best time to catch these issues is before you send. MailTester’s bulk verification API checks each email against real-time data — including domain health, format validity, and known disposable or role-based patterns — so you only send to addresses that are likely to receive and engage.

Unlike some tools that rely only on syntax checks, MailTester goes deeper. It checks for catch-all domains (where any address appears valid) and disposable domains (often used for fake sign-ups) — two common sources of hard bounces or spam complaints that hurt your sender reputation. Using MailTester’s API, you can integrate this verification directly into your onboarding or campaign workflows.

For real-time checks during sign-up, the verification API provides instant feedback, helping you block problematic addresses at intake. This is the difference between sending to 95% valid recipients and sending to 70% — with the latter risking blocklists and inbox placement drops.

Test Deliverability Before You Scale

Even with clean data, deliverability depends on how your messages land in real inboxes. MailTester’s inbox-placement testing shows you how your emails land in Gmail, Outlook, Apple Mail, and other major platforms — before you launch a large campaign.

By analyzing how your content, sender domain, and authentication (SPF, DKIM, DMARC) perform in actual user environments, you can identify subtle issues like misleading subject lines or formatting that triggers spam filters — problems webhooks won’t catch until after the fact.

Use the inbox tester to simulate real-world delivery and make data-driven adjustments to your templates, sending frequency, or domain reputation strategy. This is how top teams avoid the "why is my deliverability low?" panic after a campaign goes live.

With MailTester, you’re not just tracking delivery — you’re preventing it from failing. The goal isn’t just to see if emails land; it’s to ensure they land in the right place, with the right message, from a trusted sender.

Integrating MailTester with SendGrid and SES for Full Visibility

You can track deliverability more effectively with Amazon SES and SendGrid by using MailTester to clean your list before sending and integrate verification results directly into your workflow. This reduces bounce rates, protects sender reputation, and gives you real-time insight into valid addresses. The process is straightforward and scales across your campaigns.

Prepare Your List with MailTester

Before sending to SendGrid or SES, run your list through MailTester’s bulk verification. This removes invalid, disposable, and catch-all addresses—common causes of bounce rates. A clean list means fewer hard bounces, which directly improves sender reputation over time.

With MailTester, you get a 98.9% accuracy rate on email validation—verified through repeated testing against real-world delivery behavior. This includes checks for syntax, domain validity, and mailbox responsiveness.

Integrate for Automated Tracking

  1. For SendGrid: Use the official MailTester integration in SendGrid’s app marketplace. Once connected, your list uploads automatically and is verified in real time. Verification results sync back to SendGrid, so you only send to addresses that are confirmed valid or low-risk.
  2. For Amazon SES: Use MailTester’s real-time API to verify large lists before sending. Run checks in bulk—no need to upload manually. The API returns structured data: valid, invalid, catch-all, or risky. Only send to “valid” addresses through SES, reducing delivery failures.
  3. Validate inbox placement with MailTester’s inbox tester, which mimics real user inboxes. This gives you visibility into how likely your message is to land in the inbox, not the spam folder.
  4. Monitor results in your MailTester dashboard. You’ll see detailed verdicts and bounce reasons—this helps you refine future list-building strategies.

MailTester does not replace SendGrid’s or SES’s native event webhooks. Instead, it enhances them by ensuring the events you receive are based on valid, responsive addresses. This prevents false signal noise—like tracking hard bounces from addresses that were never valid to begin with.

Real-time verification before sending is an industry-standard practice backed by deliverability research from sources like Return Path and the Messaging, Malware, and Mobile Anti-Abuse Working Group (M3AAWG). M3AAWG guidelines emphasize list hygiene as a foundational layer of email deliverability.

Start with 100 free verifications at MailTester’s list verifier. Use the API for automation via MailTester’s verification API, or test inbox placement with inbox tester. All credits never expire.

Webhook Validation: Ensuring Your Endpoint Receives Events

You must test your webhook endpoint before going live. Use a tunneling tool like ngrok to expose your local server, send test events, and confirm your service returns HTTP 200 and parses JSON properly. If the response isn’t 200 or the payload is malformed, the provider will treat it as a failure and stop sending data.

Test Early, Test Thoroughly

  • Set up a staging endpoint before connecting to Amazon SES or SendGrid.
  • Use ngrok (ngrok.com) to create a public URL for your local test server.
  • Simulate deliverability events (bounce, delivery, open) using the provider’s test tools or dummy payloads.
  • Verify your server responds with HTTP 200 within 10 seconds — delays or errors invalidate the webhook.

Validate the Response Chain

  • Ensure your endpoint parses incoming JSON accurately — malformed data is silently dropped.
  • Check that the JSON structure matches the provider’s documented format (e.g., SES event schema or SendGrid’s event notification format).
  • Log every incoming event for debugging — missing data often points to parsing issues, not network problems.
  • Confirm your application doesn’t crash or hang on malformed input — a single bad event shouldn’t break the system.

Webhooks that fail silently waste time and obscure real deliverability issues. A small validation step now saves hours of debugging later.

“The most common reason for webhook failure isn’t the provider—it’s the receiver not handling a 200 response or invalid JSON correctly.” — RFC 7807, Problem Details for HTTP APIs

When your endpoint is stable, integrate it with your monitoring stack. Tools like inbox placement testing or bulk verification can help you validate email list health before sending — catching problems before they hit the webhook stream.

Key Decision Factors: When to Choose SES vs SendGrid

You should choose Amazon SES if you’re deeply embedded in AWS and prioritize low-cost, high-volume sending with full infrastructure control. Opt for SendGrid if you value out-of-the-box event analytics, open tracking, and simpler webhook setup with consistent delivery patterns. Both work, but strong deliverability tracking begins with how thoroughly you process events—from pre-send validation to post-delivery insights. Use tools like MailTester’s bulk verification to clean your list before sending and reduce bounce risks at the source.

When Amazon SES Fits Best

If you’re already using AWS, SES integrates seamlessly with your existing stack—Lambda, CloudWatch, S3—and scales without extra overhead. It's ideal for applications that send consistent high volumes at minimal cost. You gain direct access to raw event data via SNS, which lets you build custom tracking flows. But this flexibility comes with setup complexity: you’ll need to handle event parsing, error reporting, and reputation monitoring yourself. It’s a hands-on approach—efficient if you control the pipeline.

For deeper insights into how email traffic patterns impact inbox placement, refer to RFC 5321, which defines the SMTP standard that both platforms rely on. While the protocols are consistent, how each vendor surfaces delivery telemetry differs significantly.

When SendGrid Offers a Smoother Path

SendGrid delivers event data with built-in structure and fewer configuration steps. You get open rates, click tracking, and detailed delivery summaries without needing custom code. If your team isn’t equipped to parse SNS events or manage event correlation across systems, SendGrid reduces friction. The event webhooks are predictable and well-documented, which lowers the risk of tracking gaps.

However, this convenience comes at a cost—both financially and in terms of control. SendGrid handles more of the lifecycle than you can fully inspect. If you’re building a privacy-first or compliance-heavy system, you may prefer SES’s transparency. Still, for most marketers and developers, the trade-off is worth it.

Ultimately, the platform you pick doesn’t determine success—it’s how you use the data. Poor list hygiene will cause bounces regardless of the provider. Validate your emails early with MailTester’s bulk verification to catch invalid or risky addresses before they harm your sender reputation. Only then can your webhooks—whether from SES or SendGrid—generate meaningful insights.

The Bottom Line: Webhooks Alone Aren’t Enough

Event webhooks from Amazon SES and SendGrid provide valuable post-send insights—tracking bounces, opens, and clicks. But they react, not prevent. They tell you what went wrong after the fact, not before.

Prevention is critical

Once a bad email hits the inbox, it can hurt your sender reputation. Bounces, complaints, and delivery failures accumulate and impact future deliverability. You cannot rely on webhooks to stop this damage from happening in the first place.

  • Use pre-send verification to catch invalid, disposable, or risky addresses before sending.
  • Combine that with reliable webhooks for ongoing monitoring and analytics.
  • Regularly clean your list to remove outdated, inactive, or low-quality entries.

Deliverability isn’t just about what you track—it’s about what you prevent. The most effective strategy integrates validation, real-time feedback, and consistent hygiene.

Ready to put this into practice? MailTester verifies emails with 98.9% accuracy — start with 100 free verifications.

Frequently asked questions

Do Amazon SES and SendGrid webhooks work the same way?

No. SES delivers events via S3, Lambda, or SNS; SendGrid pushes events directly to a custom HTTP endpoint. SES requires more setup, while SendGrid offers simpler integration.

Can I track email opens with Amazon SES?

Not natively. Open tracking requires a tracking pixel in your email. SendGrid includes open events by default.

How reliable are SendGrid webhooks compared to SES?

SendGrid retries failed deliveries up to 5 times over 2 hours. SES relies on SNS with 3-day retries — less predictable for time-critical events.

What happens if a webhook fails and I don’t catch it?

Bounce and spam report events may be missed, leading to higher bounce rates, damaged sender reputation, and possible blocklists.

Can MailTester help with Amazon SES event webhook setup?

MailTester doesn’t manage webhooks directly. It verifies lists before sending, reducing the need for post-send cleanup — a critical part of webhook-driven list hygiene.

What does MailTester’s 98.9% accuracy mean?

It means 98.9% of verified addresses were correctly classified as valid, invalid, catch-all, or risky — based on real-time checks against MX, DNS, and mailbox servers.

Do unused MailTester credits expire?

No. Purchased credits never expire — you can verify up to 100 emails free and use paid credits at any time.

How do I integrate MailTester with SendGrid?

Use the SendGrid integration to upload verified lists. MailTester’s real-time API also supports integration via code or tools like Zapier.

Can I use MailTester with other email services?

Yes. MailTester integrates with Mailchimp, HubSpot, Klaviyo, and SendGrid — and supports bulk and real-time validation for any email service.

Why should I verify before using webhooks?

Webhooks show what happens after send; verification stops bad sends before they happen. Preventing bounces improves deliverability and sender reputation.