Webhooks

Webhooks allow you to receive real-time notifications about email events in your application. This guide covers creating, managing, and verifying webhooks with the Resend Go SDK.

Overview

Resend webhooks notify your application when events occur, such as:

Emails being sent, delivered, or bounced
Contacts being created, updated, or deleted
Domains being created, updated, or deleted

The Go SDK provides built-in webhook signature verification using HMAC-SHA256 to ensure webhook authenticity.

Webhook Events

Resend supports the following webhook events:

Email Events

email.sent

string

Triggered when an email is successfully accepted for delivery

email.delivered

string

Triggered when an email is successfully delivered to the recipient’s mail server

email.delivery_delayed

string

Triggered when email delivery is temporarily delayed

email.complained

string

Triggered when a recipient marks an email as spam

email.bounced

string

Triggered when an email bounces (hard or soft bounce)

email.opened

string

Triggered when a recipient opens an email (requires open tracking)

email.clicked

string

Triggered when a recipient clicks a link in an email (requires click tracking)

email.received

string

Triggered when an inbound email is received

email.failed

string

Triggered when email sending fails

Contact Events

contact.created

string

Triggered when a new contact is created

contact.updated

string

Triggered when a contact is updated

contact.deleted

string

Triggered when a contact is deleted

Domain Events

domain.created

string

Triggered when a new domain is created

domain.updated

string

Triggered when a domain is updated

domain.deleted

string

Triggered when a domain is deleted

Creating a Webhook

Create a webhook to start receiving events at your endpoint.

import (
    "github.com/resend/resend-go/v3"
)

client := resend.NewClient("re_123456789")

params := &resend.CreateWebhookRequest{
    Endpoint: "https://your-app.com/webhooks/resend",
    Events: []string{
        resend.EventEmailSent,
        resend.EventEmailDelivered,
        resend.EventEmailBounced,
    },
}

webhook, err := client.Webhooks.Create(params)
if err != nil {
    panic(err)
}

fmt.Println("Webhook ID:", webhook.Id)
fmt.Println("Signing Secret:", webhook.SigningSecret)

Save the signing secret! The SigningSecret is only returned when creating a webhook. Store it securely - you’ll need it to verify webhook signatures.

Retrieving a Webhook

Get details about a specific webhook.

Get Webhook

webhook, err := client.Webhooks.Get("wh_123456")
if err != nil {
    panic(err)
}

fmt.Println("Status:", webhook.Status)
fmt.Println("Endpoint:", webhook.Endpoint)
fmt.Println("Events:", webhook.Events)
fmt.Println("Created:", webhook.CreatedAt)

Listing Webhooks

Retrieve all webhooks in your account with optional pagination.

webhooks, err := client.Webhooks.List()
if err != nil {
    panic(err)
}

fmt.Printf("You have %d webhook(s)\n", len(webhooks.Data))

for i, wh := range webhooks.Data {
    fmt.Printf("[%d] %s - %s\n", i+1, wh.Id, wh.Status)
    fmt.Printf("    Endpoint: %s\n", wh.Endpoint)
    fmt.Printf("    Events: %v\n", wh.Events)
}

Updating a Webhook

Update webhook configuration including endpoint, events, and status.

newEndpoint := "https://new-api.example.com/webhook"

updateParams := &resend.UpdateWebhookRequest{
    Endpoint: &newEndpoint,
}

updated, err := client.Webhooks.Update("wh_123456", updateParams)
if err != nil {
    panic(err)
}

fmt.Println("Updated webhook:", updated.Id)

Disable webhooks temporarily instead of deleting them if you need to pause event notifications.

Deleting a Webhook

Remove a webhook from your account.

Delete Webhook

deleted, err := client.Webhooks.Remove("wh_123456")
if err != nil {
    panic(err)
}

fmt.Printf("Webhook %s deleted: %v\n", deleted.Id, deleted.Deleted)

Receiving and Verifying Webhooks

Webhooks are sent as POST requests to your endpoint. Always verify webhook signatures to ensure they’re from Resend.

Webhook Headers

Resend includes three important headers with each webhook:

svix-id

string

Unique identifier for the webhook message

svix-timestamp

string

Unix timestamp when the webhook was sent

svix-signature

string

HMAC-SHA256 signature for verifying authenticity

Verification Method

The SDK provides a Verify method that implements HMAC-SHA256 signature verification:

Webhook Receiver

import (
    "encoding/json"
    "io"
    "log"
    "net/http"
    
    "github.com/resend/resend-go/v3"
)

func webhookHandler(client *resend.Client, webhookSecret string) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        // 1. Read the raw request body
        body, err := io.ReadAll(r.Body)
        if err != nil {
            log.Printf("Error reading body: %v", err)
            http.Error(w, "Failed to read request body", http.StatusBadRequest)
            return
        }
        defer r.Body.Close()

        // 2. Extract webhook headers
        headers := resend.WebhookHeaders{
            Id:        r.Header.Get("svix-id"),
            Timestamp: r.Header.Get("svix-timestamp"),
            Signature: r.Header.Get("svix-signature"),
        }

        // 3. Verify the webhook signature
        err = client.Webhooks.Verify(&resend.VerifyWebhookOptions{
            Payload:       string(body),
            Headers:       headers,
            WebhookSecret: webhookSecret,
        })

        if err != nil {
            log.Printf("Webhook verification failed: %v", err)
            http.Error(w, "Webhook verification failed", http.StatusBadRequest)
            return
        }

        // 4. Parse the verified payload
        var payload map[string]any
        if err := json.Unmarshal(body, &payload); err != nil {
            log.Printf("Error parsing JSON: %v", err)
            http.Error(w, "Invalid JSON payload", http.StatusBadRequest)
            return
        }

        // 5. Process the webhook event
        eventType := payload["type"].(string)
        log.Printf("✓ Verified webhook: %s", eventType)
        
        // Handle different event types
        switch eventType {
        case resend.EventEmailSent:
            handleEmailSent(payload)
        case resend.EventEmailDelivered:
            handleEmailDelivered(payload)
        case resend.EventEmailBounced:
            handleEmailBounced(payload)
        default:
            log.Printf("Unhandled event type: %s", eventType)
        }

        // 6. Respond with success
        w.WriteHeader(http.StatusOK)
        json.NewEncoder(w).Encode(map[string]bool{"success": true})
    }
}

How Verification Works

The Verify method implements the following security checks:

Timestamp Validation

Verifies the webhook timestamp is within 5 minutes to prevent replay attacks.

// Checks if timestamp is within tolerance window
diff := now - timestamp
if diff > 300 seconds {
    return error
}

Signature Construction

Constructs the signed content from the webhook data:

signedContent = "{id}.{timestamp}.{payload}"

HMAC-SHA256 Calculation

Computes the expected signature using your webhook secret:

h := hmac.New(sha256.New, decodedSecret)
h.Write([]byte(signedContent))
expectedSignature := base64.StdEncoding.EncodeToString(h.Sum(nil))

Constant-Time Comparison

Safely compares signatures to prevent timing attacks:

if subtle.ConstantTimeCompare(expected, received) == 1 {
    return nil // Valid
}

Complete HTTP Server Example

Here’s a complete example of a webhook receiver server:

Webhook Server

package main

import (
    "encoding/json"
    "fmt"
    "io"
    "log"
    "net/http"
    "os"
    
    "github.com/resend/resend-go/v3"
)

func main() {
    webhookSecret := os.Getenv("RESEND_WEBHOOK_SECRET")
    apiKey := os.Getenv("RESEND_API_KEY")
    
    client := resend.NewClient(apiKey)

    http.HandleFunc("/webhook", func(w http.ResponseWriter, r *http.Request) {
        if r.Method != http.MethodPost {
            http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
            return
        }

        // Read raw body (required for signature verification)
        body, err := io.ReadAll(r.Body)
        if err != nil {
            log.Printf("Error reading body: %v", err)
            http.Error(w, "Failed to read request body", http.StatusBadRequest)
            return
        }
        defer r.Body.Close()

        // Extract Svix headers
        headers := resend.WebhookHeaders{
            Id:        r.Header.Get("svix-id"),
            Timestamp: r.Header.Get("svix-timestamp"),
            Signature: r.Header.Get("svix-signature"),
        }

        // Verify the webhook
        err = client.Webhooks.Verify(&resend.VerifyWebhookOptions{
            Payload:       string(body),
            Headers:       headers,
            WebhookSecret: webhookSecret,
        })

        if err != nil {
            log.Printf("Webhook verification failed: %v", err)
            http.Error(w, "Webhook verification failed", http.StatusBadRequest)
            return
        }

        // Parse the verified payload
        var payload map[string]any
        if err := json.Unmarshal(body, &payload); err != nil {
            log.Printf("Error parsing JSON: %v", err)
            http.Error(w, "Invalid JSON payload", http.StatusBadRequest)
            return
        }

        log.Printf("✓ Webhook verified successfully!")
        log.Printf("Event Type: %v", payload["type"])
        
        // Extract common fields
        eventType, _ := payload["type"].(string)
        data, _ := payload["data"].(map[string]any)
        
        // Handle specific events
        switch eventType {
        case resend.EventEmailSent:
            emailId, _ := data["email_id"].(string)
            log.Printf("Email sent: %s", emailId)
            
        case resend.EventEmailDelivered:
            emailId, _ := data["email_id"].(string)
            log.Printf("Email delivered: %s", emailId)
            
        case resend.EventEmailBounced:
            emailId, _ := data["email_id"].(string)
            bounceType, _ := data["bounce_type"].(string)
            log.Printf("Email bounced: %s (type: %s)", emailId, bounceType)
            
        case resend.EventContactCreated:
            contactId, _ := data["contact_id"].(string)
            email, _ := data["email"].(string)
            log.Printf("Contact created: %s (%s)", contactId, email)
            
        default:
            log.Printf("Unhandled event: %s", eventType)
        }

        // Respond with success
        w.Header().Set("Content-Type", "application/json")
        w.WriteHeader(http.StatusOK)
        json.NewEncoder(w).Encode(map[string]bool{"success": true})
    })

    port := ":5000"
    fmt.Printf("🚀 Webhook receiver listening on http://localhost%s/webhook\n", port)
    
    if err := http.ListenAndServe(port, nil); err != nil {
        log.Fatal(err)
    }
}

Event Payload Examples

Here are examples of webhook payloads for different events:

email.sent

{
  "type": "email.sent",
  "created_at": "2024-01-15T10:30:00.000Z",
  "data": {
    "email_id": "4ef2e6e9-8e0a-4c3e-9c42-3c1e3b7a4f3e",
    "from": "[email protected]",
    "to": ["[email protected]"],
    "subject": "Welcome to our platform"
  }
}

email.delivered

{
  "type": "email.delivered",
  "created_at": "2024-01-15T10:31:00.000Z",
  "data": {
    "email_id": "4ef2e6e9-8e0a-4c3e-9c42-3c1e3b7a4f3e",
    "from": "[email protected]",
    "to": ["[email protected]"],
    "subject": "Welcome to our platform"
  }
}

email.bounced

{
  "type": "email.bounced",
  "created_at": "2024-01-15T10:31:30.000Z",
  "data": {
    "email_id": "4ef2e6e9-8e0a-4c3e-9c42-3c1e3b7a4f3e",
    "from": "[email protected]",
    "to": ["[email protected]"],
    "subject": "Welcome to our platform",
    "bounce_type": "hard",
    "bounce_reason": "Mailbox does not exist"
  }
}

contact.created

{
  "type": "contact.created",
  "created_at": "2024-01-15T10:32:00.000Z",
  "data": {
    "contact_id": "c4f8e2a1-7b3c-4d5e-9f8a-1b2c3d4e5f6a",
    "email": "[email protected]",
    "first_name": "John",
    "last_name": "Doe"
  }
}

Error Handling

Robust Webhook Verification

func verifyWebhook(client *resend.Client, secret string, r *http.Request) error {
    body, err := io.ReadAll(r.Body)
    if err != nil {
        return fmt.Errorf("failed to read body: %w", err)
    }

    headers := resend.WebhookHeaders{
        Id:        r.Header.Get("svix-id"),
        Timestamp: r.Header.Get("svix-timestamp"),
        Signature: r.Header.Get("svix-signature"),
    }

    // Verify all required headers are present
    if headers.Id == "" || headers.Timestamp == "" || headers.Signature == "" {
        return fmt.Errorf("missing required webhook headers")
    }

    // Verify the signature
    err = client.Webhooks.Verify(&resend.VerifyWebhookOptions{
        Payload:       string(body),
        Headers:       headers,
        WebhookSecret: secret,
    })

    if err != nil {
        return fmt.Errorf("verification failed: %w", err)
    }

    return nil
}

Best Practices

Always Verify Signatures

Never process webhooks without verifying their signature to prevent spoofing attacks.

Use HTTPS Endpoints

Always use HTTPS endpoints for webhooks to ensure data is encrypted in transit.

Respond Quickly

Return a 200 OK response immediately and process events asynchronously.

Handle Retries

Implement idempotency to handle duplicate webhook deliveries gracefully.

Store Signing Secrets Securely

Store webhook secrets in environment variables or secret management systems.

Monitor Webhook Health

Log webhook events and set up alerts for verification failures.

Testing Webhooks

Use ngrok for Local Testing

Expose your local server to the internet:

ngrok http 5000

Then create a webhook with the ngrok URL:

webhook, err := client.Webhooks.Create(&resend.CreateWebhookRequest{
    Endpoint: "https://your-ngrok-url.ngrok.io/webhook",
    Events:   []string{resend.EventEmailSent},
})

Send Test Emails

Trigger webhook events by sending test emails:

_, err := client.Emails.Send(&resend.SendEmailRequest{
    From:    "[email protected]",
    To:      []string{"[email protected]"},
    Subject: "Test Webhook",
    Html:    "<p>Testing webhooks</p>",
})

Monitor Logs

Watch your server logs to see webhook events arriving:

✓ Webhook verified successfully!
Event Type: email.sent
Email sent: 4ef2e6e9-8e0a-4c3e-9c42-3c1e3b7a4f3e

Next Steps

Email Events

Learn about sending emails and triggering events

Broadcasts

Send campaigns and receive broadcast events

Webhook Example

View the complete webhook receiver example

API Reference

View the complete Webhooks API reference

Get Started

Core Features

Advanced

Examples

Overview

Webhook Events

Email Events

Contact Events

Domain Events

Creating a Webhook

Retrieving a Webhook

Listing Webhooks

Updating a Webhook

Deleting a Webhook

Receiving and Verifying Webhooks

Webhook Headers

Verification Method

How Verification Works

Complete HTTP Server Example

Event Payload Examples

Error Handling

Best Practices

Always Verify Signatures

Use HTTPS Endpoints

Respond Quickly

Handle Retries

Store Signing Secrets Securely

Monitor Webhook Health

Testing Webhooks

Next Steps

Email Events

Broadcasts

Webhook Example

API Reference

Build docs developers (and LLMs) love

Get Started

Core Features

Advanced

Examples

​Overview

​Webhook Events

​Email Events

​Contact Events

​Domain Events

​Creating a Webhook

​Retrieving a Webhook

​Listing Webhooks

​Updating a Webhook

​Deleting a Webhook

​Receiving and Verifying Webhooks

​Webhook Headers

​Verification Method

​How Verification Works

​Complete HTTP Server Example

​Event Payload Examples

​Error Handling

​Best Practices

Always Verify Signatures

Use HTTPS Endpoints

Respond Quickly

Handle Retries

Store Signing Secrets Securely

Monitor Webhook Health

​Testing Webhooks

​Next Steps

Email Events

Broadcasts

Webhook Example

API Reference

Build docs developers (and LLMs) love

Overview

Webhook Events

Email Events

Contact Events

Domain Events

Creating a Webhook

Retrieving a Webhook

Listing Webhooks

Updating a Webhook

Deleting a Webhook

Receiving and Verifying Webhooks

Webhook Headers

Verification Method

How Verification Works

Complete HTTP Server Example

Event Payload Examples

Error Handling

Best Practices

Testing Webhooks

Next Steps