lettr-go

The official Go SDK for the Lettr Email API. A typed client for emails, templates, domains, webhooks, audience, and campaigns.

Installation

go get github.com/lettr-com/lettr-go

Requires Go 1.21 or later.

Quick Start

package main

import (
	"context"
	"fmt"
	"log"

	lettr "github.com/lettr-com/lettr-go"
)

func main() {
	client := lettr.NewClient("your-api-key")

	resp, err := client.Emails.Send(context.Background(), &lettr.SendEmailRequest{
		From:    "sender@example.com",
		To:      []string{"recipient@example.com"},
		Subject: "Hello from Lettr",
		Html:    "<h1>Hello!</h1>",
	})
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("Email sent! Request ID: %s\n", resp.Data.RequestID)
}

Methods return a wrapped response (read resp.Data) and a structured error.

Error Handling

The SDK returns typed errors you can inspect with helper predicates:

resp, err := client.Emails.Send(ctx, req)
if err != nil {
	switch {
	case lettr.IsValidationError(err):
		apiErr := err.(*lettr.Error)
		for field, messages := range apiErr.Errors {
			fmt.Printf("%s: %v\n", field, messages)
		}
	case lettr.IsUnauthorized(err):
		fmt.Println("Invalid API key")
	case lettr.IsNotFound(err):
		fmt.Println("Resource not found")
	default:
		fmt.Printf("Error: %v\n", err)
	}
}

See Error Handling for the full set of predicates.

Documentation

Full guides for every service, with complete request/response details, live in the docs:

📚 docs.lettr.com/quickstart/go

Topic	Guide
Install, client, sending	Quickstart
Batch sending, context & timeouts, error handling	Advanced
Manage Lettr templates & merge tags	Templates
Add, verify, and manage sending domains	Domains
Webhook endpoints for delivery & engagement events	Webhooks
Lists, contacts, topics, properties, segments	Audience
List, send, and schedule campaigns	Campaigns
Endpoint reference (params & schemas)	API Reference

Versioning & Releases

• Version history: CHANGELOG.md
• Release process: RELEASING.md

This project follows Semantic Versioning.

License

MIT