Send email in Go

export TINYRELAY_API_KEY="your-api-key"

$env:TINYRELAY_API_KEY = "your-api-key"

package main

type Address struct {
	Name  string `json:"name,omitempty"`
	Email string `json:"email"`
}

type Recipient struct {
	Name       string            `json:"name,omitempty"`
	Email      string            `json:"email"`
	Attributes map[string]string `json:"attributes,omitempty"`
	Metadata   map[string]string `json:"metadata,omitempty"`
}

type Sender struct {
	From    Address  `json:"from"`
	ReplyTo *Address `json:"replyTo,omitempty"`
}

type Recipients struct {
	To []Recipient `json:"to"`
}

type Email struct {
	Subject    string            `json:"subject"`
	Body       string            `json:"body"`
	Sender     Sender            `json:"sender"`
	Recipients Recipients        `json:"recipients"`
	CampaignID string            `json:"campaignId,omitempty"`
	Metadata   map[string]string `json:"metadata,omitempty"`
}

var alert = Email{
	Subject: "New sign-in to your Acme account",
	Body:    "<p>Hi [FIRST_NAME], we noticed a new sign-in to your account.</p>",
	Sender:  Sender{From: Address{Name: "Acme Security", Email: "security@acme.com"}},
	Recipients: Recipients{To: []Recipient{{
		Name:       "Ann Lee",
		Email:      "ann@example.com",
		Attributes: map[string]string{"FIRST_NAME": "Ann"},
	}}},
	Metadata: map[string]string{"tenant_id": "acme", "event": "new_sign_in"},
}

alert := map[string]any{
	"subject": "New sign-in to your Acme account",
	"body":    "<p>Hi [FIRST_NAME], we noticed a new sign-in to your account.</p>",
	"sender": map[string]any{
		"from": map[string]string{"name": "Acme Security", "email": "security@acme.com"},
	},
	"recipients": map[string]any{
		"to": []map[string]any{{
			"email":      "ann@example.com",
			"attributes": map[string]string{"FIRST_NAME": "Ann"},
		}},
	},
	"metadata": map[string]string{"tenant_id": "acme", "event": "new_sign_in"},
}

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"time"
)

const apiURL = "https://api.tinyemail.com/v1/relay/email/campaign"

// Reuse one client; the zero-value client has no timeout.
var client = &http.Client{Timeout: 10 * time.Second}

type SendResponse struct {
	RequestID string `json:"requestId"`
	Message   string `json:"message"`
}

func send(email any) (string, error) {
	payload, err := json.Marshal(email)
	if err != nil {
		return "", err
	}

	req, err := http.NewRequest(http.MethodPost, apiURL, bytes.NewReader(payload))
	if err != nil {
		return "", err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("X-RELAY-ACCESS-TOKEN", os.Getenv("TINYRELAY_API_KEY"))

	resp, err := client.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return "", err
	}
	if resp.StatusCode != http.StatusAccepted {
		return "", fmt.Errorf("tinyRelay %d: %s", resp.StatusCode, body)
	}

	var out SendResponse
	if err := json.Unmarshal(body, &out); err != nil {
		return "", err
	}
	return out.RequestID, nil
}

func main() {
	id, err := send(alert)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	fmt.Println("accepted:", id)
}

{
  "requestId": "833c5151-5a98-4bad-a30f-7cc816352b7a",
  "message": "SUCCESS"
}

to := make([]Recipient, 0, len(users))
for _, u := range users {
	to = append(to, Recipient{
		Email:      u.Email,
		Attributes: map[string]string{"FIRST_NAME": u.FirstName},
		Metadata:   map[string]string{"user_id": u.ID},
	})
}

id, err := send(Email{
	Subject:    "New sign-in to your Acme account",
	Body:       "<p>Hi [FIRST_NAME], we noticed a new sign-in to your account.</p>",
	Sender:     Sender{From: Address{Name: "Acme Security", Email: "security@acme.com"}},
	Recipients: Recipients{To: to},
	Metadata:   map[string]string{"tenant_id": "acme", "event": "new_sign_in"},
})