Sending email in Go: a complete guide to libraries and tools

Sending email in Go (Golang): overview of libraries and tools

Go (Golang) is a modern compiled language that is excellent for building backend services, microservices, and automation. One common task is programmatically sending emails. In this article, we will thoroughly examine Go's standard tools for working with SMTP, popular third-party libraries, as well as examples of sending plain text and HTML emails with attachments.

Standard package net/smtp

The Go standard library includes the net/smtp package, which provides basic capabilities for sending email via an SMTP server. It is simple but requires manual construction of the email body (including headers, MIME types).

Simple example of sending a text email

package main

import (    "fmt"    "net/smtp")

func main() {    // Authentication data    from := "your_email@gmail.com"    password := "your_app_password"    to := []string{"recipient@example.com"}

    // SMTP server (e.g., Gmail)    smtpHost := "smtp.gmail.com"    smtpPort := "587"

    // Email body (must include headers)    subject := "Subject: Hello from Go!"    body := "This is a test email sent using net/smtp."    message := []byte(subject + "" + body)

    // Authentication    auth := smtp.PlainAuth("", from, password, smtpHost)

    // Sending    err := smtp.SendMail(smtpHost+":"+smtpPort, auth, from, to, message)    if err != nil {        fmt.Println("Error sending:", err)        return    }    fmt.Println("Email sent successfully!")}

Important: For Gmail, you will need an app password, not your regular password.

Sending HTML emails and emails with attachments

The net/smtp package cannot automatically form MIME messages. For HTML emails or attachments, you will have to manually compose the Content-Type headers and encode attachments in base64. This is cumbersome, so for complex emails it is better to use third-party libraries.

Popular third-party libraries for sending email in Go

There are several mature libraries that significantly simplify the work:

• go-gomail/gomail — one of the most popular. Supports HTML, attachments, image embedding, multiple recipients.
• jordan-wright/email — a lightweight library with a convenient API.
• sendgrid/sendgrid-go — the official client for the SendGrid service (suitable for mass mailings).

Example with go-gomail

package main

import (    "fmt"    "gopkg.in/gomail.v2")

func main() {    m := gomail.NewMessage()    m.SetHeader("From", "your_email@gmail.com")    m.SetHeader("To", "recipient@example.com")    m.SetHeader("Subject", "HTML email with attachment")    m.SetBody("text/html", "<h1>Hello!</h1><p>This is an <b>HTML</b> email.</p>")    m.Attach("/path/to/file.pdf") // Attachment

    d := gomail.NewDialer("smtp.gmail.com", 587, "your_email@gmail.com", "your_app_password")

    if err := d.DialAndSend(m); err != nil {        fmt.Println("Error:", err)        return    }    fmt.Println("Email sent!")}

Asynchronous sending and connection pooling

If you need to send many emails (for example, after user registration), it is important not to block the main thread. Go handles concurrency excellently: