# Send email with Go

> Send email from Go with the emailit-go SDK or net/smtp, handle API errors, and verify Emailit webhook signatures in a net/http handler.

This guide shows how to send email from a Go service with the official `emailit-go` SDK, how to use `net/smtp` instead, and how to verify webhooks in a `net/http` handler.

## Prerequisites

- Go 1.21 or later.
- A [verified sending domain](/docs/domains/add-a-domain/), for example `acme.com`.
- An [API key](/docs/developers/api-keys/). A Sending Only key restricted to your domain is enough.
- Until your workspace has [production access](/docs/workspaces/production-access/), you can only send to the account emails of workspace members.

## Install the SDK

```bash
go get github.com/emailit/emailit-go/v2
```

The SDK only depends on the Go standard library.

## Configure your API key

Pass the key to your process as an environment variable:

```bash
```

## Send an email

```go title="main.go"
package main

	"log"
	"os"

	"github.com/emailit/emailit-go/v2"
)

func main() {
	client := emailit.NewClient(os.Getenv("EMAILIT_API_KEY"))

	email, err := client.Emails.Send(&emailit.SendEmailRequest{
		From:    "Acme <hello@acme.com>",
		To:      []string{"ada@example.com"},
		Subject: "Your login code",
		Text:    "Your code is 482913. It expires in 10 minutes.",
		Html:    "<p>Your code is <strong>482913</strong>. It expires in 10 minutes.</p>",
	})
	if err != nil {
		log.Fatal(err)
	}

	log.Println("sent", email.Id) // em_…
}
```

Create the client once and share it; it's safe to reuse across requests. To send a stored template, set `Template` to its alias or `tem_` ID and pass `Variables`. To change timeouts, pass your own client: `emailit.NewClient(key, emailit.WithHTTPClient(&http.Client{Timeout: 10 * time.Second}))`.

### Handle errors

The SDK returns ordinary Go errors with helpers to classify them:

```go
email, err := client.Emails.Send(req)
if err != nil {
	switch {
	case emailit.IsRateLimitError(err):
		// 429: back off and retry
	case emailit.IsAuthenticationError(err):
		// 401: the API key is missing or invalid
	case emailit.IsUnprocessableEntityError(err):
		// 422: for example, the from domain isn't verified
	}

	var apiErr *emailit.APIError
	if errors.As(err, &apiErr) {
		log.Printf("emailit: %d %s", apiErr.StatusCode, apiErr.Message)
	}
	return err
}
```

## Send with SMTP instead

The standard library's `net/smtp` can send through the Emailit relay. `smtp.SendMail` upgrades the connection with STARTTLS before it authenticates:

```go title="smtp.go"
package main

	"log"
	"net/smtp"
	"os"
	"strings"
)

func main() {
	auth := smtp.PlainAuth("", "emailit", os.Getenv("EMAILIT_API_KEY"), "smtp.emailit.com")

	msg := strings.Join([]string{
		"From: Acme <hello@acme.com>",
		"To: ada@example.com",
		"Subject: Your login code",
		"MIME-Version: 1.0",
		"Content-Type: text/plain; charset=UTF-8",
		"",
		"Your code is 482913. It expires in 10 minutes.",
	}, "\r\n")

	err := smtp.SendMail("smtp.emailit.com:587", auth, "hello@acme.com", []string{"ada@example.com"}, []byte(msg))
	if err != nil {
		log.Fatal(err)
	}
}
```

`net/smtp` is minimal: you build the message yourself, and it has no implicit TLS on port 465. For HTML, attachments or connection reuse, use a maintained mail library or the API. If port 587 is blocked, use `smtp.emailit.com:2525`. See [SMTP settings](/docs/smtp/settings/).

## Receive webhooks

[Create a webhook](/docs/webhooks/set-up/) and store its signing secret in `EMAILIT_WEBHOOK_SECRET`. The handler reads the raw body, checks the signature, then decodes the array of events:

```go title="webhooks.go"
package main

	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"io"
	"net/http"
	"os"
	"strconv"
	"time"
)

type emailitEvent struct {
	EventID string `json:"event_id"`
	Type    string `json:"type"`
	Data    struct {
		Object map[string]any `json:"object"`
	} `json:"data"`
}

func validSignature(body []byte, signature, timestamp, secret string) bool {
	ts, err := strconv.ParseInt(timestamp, 10, 64)
	if err != nil || signature == "" {
		return false
	}
	if age := time.Now().Unix() - ts; age > 300 || age < -300 {
		return false
	}
	mac := hmac.New(sha256.New, []byte(secret))
	mac.Write([]byte(timestamp + "."))
	mac.Write(body)
	expected := hex.EncodeToString(mac.Sum(nil))
	return hmac.Equal([]byte(expected), []byte(signature))
}

func emailitWebhook(w http.ResponseWriter, r *http.Request) {
	body, err := io.ReadAll(http.MaxBytesReader(w, r.Body, 10<<20))
	if err != nil {
		http.Error(w, "bad request", http.StatusBadRequest)
		return
	}

	if !validSignature(body, r.Header.Get("X-Emailit-Signature"), r.Header.Get("X-Emailit-Timestamp"), os.Getenv("EMAILIT_WEBHOOK_SECRET")) {
		http.Error(w, "invalid signature", http.StatusUnauthorized)
		return
	}

	var events []emailitEvent // up to 100 events per request
	if err := json.Unmarshal(body, &events); err != nil {
		http.Error(w, "bad request", http.StatusBadRequest)
		return
	}

	for _, event := range events {
		if event.Type == "email.bounced" {
			// Stop emailing event.Data.Object["to"].
		}
	}

	w.WriteHeader(http.StatusOK)
}

func main() {
	http.HandleFunc("POST /webhooks/emailit", emailitWebhook)
	http.ListenAndServe(":8080", nil)
}
```

The `POST /path` pattern needs Go 1.22 or later; on Go 1.21, register `/webhooks/emailit` and check `r.Method` yourself. Return a `2xx` within 30 seconds; other responses are retried. See [Request signature](/docs/webhooks/request-signature/).

## Production tips

- **Stay under your rate limit.** New workspaces can send 2 emails per second and 5,000 per day by default. Send bulk mail from a worker with a rate limiter such as `golang.org/x/time/rate`. See [Limits](/docs/limits/).
- **Make retries safe.** If you retry after a timeout, send an `Idempotency-Key` header with `net/http` so the email isn't sent twice. See [Idempotency](/docs/email-api/idempotency/).
- **Deduplicate webhooks** by storing each `EventID` you process.
- **Set timeouts.** Use a context or an HTTP client timeout so a slow network doesn't hold request goroutines.

## Next steps

  - [Send email with the API](/docs/email-api/send-email/): Attachments, scheduling and tracking.
  - [Rate limits](/docs/api-reference/rate-limits/): Headers and how to back off.
  - [Webhook event types](/docs/webhooks/event-types/): Every event and its payload.
  - [SDKs and libraries](/docs/sdks/): All official libraries.

---
Source: https://emailit.com/docs/frameworks/go/