Send email using Go (Golang) via GMail with net/smtp

smtp-gmail-send.go

package main

import (
	"log"
	"net/smtp"
)

func main() {
	send("hello there")
}

func send(body string) {
	from := "...@gmail.com"
	pass := "..."
	to := "foobarbazz@mailinator.com"

	msg := "From: " + from + "\n" +
		"To: " + to + "\n" +
		"Subject: Hello there\n\n" +
		body

	err := smtp.SendMail("smtp.gmail.com:587",
		smtp.PlainAuth("", from, pass, "smtp.gmail.com"),
		from, []string{to}, []byte(msg))

	if err != nil {
		log.Printf("smtp error: %s", err)
		return
	}
	
	log.Print("sent, visit http://foobarbazz.mailinator.com")
}

gmail users: if you've seen this error: "https://support.google.com/mail/?p=InvalidSecondFactor", it means make an App Password

@ashishtiwari1993 That worked great for me, thanks!

can anyone help me to change the display name of the sender i.e if I am sending mail from xyz@gmail.com so I am seeing xyz@gmail.com in the mail list of receiver inbox but I want my custom sender name instead of xyz@gmail.com,
I am using SMTP plain auth

from:= xyz@gmail.com
auth := smtp.PlainAuth("", from, password, smtpHost)
smtp.SendMail(smtpHost+":"+smtpPort, auth, from, to, body.Bytes())

package main

import (
	"log"
	"net/smtp"
	"errors"
)

type loginAuth struct {
  username, password string
}

func LoginAuth(username, password string) smtp.Auth {
	return &loginAuth{username, password}
}

func (a *loginAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
	return "LOGIN", []byte{}, nil
}

func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
	if more {
		switch string(fromServer) {
		case "Username:":
			return []byte(a.username), nil
		case "Password:":
			return []byte(a.password), nil
		default:
			return nil, errors.New("Unkown fromServer")
		}
	}
	return nil, nil
}

func main() {
	// Choose auth method and set it up
	auth := LoginAuth("user","pass")

	// Here we do it all: connect to our server, set up a message and send it
	to := []string{"to@example.com"}
	msg := []byte("To: to@example.com\r\n" +
		"Subject: New Hack\r\n" +
		"\r\n" +
		"Wonderful solution\r\n")
	err := smtp.SendMail("smtp.gmail.com:587", auth, "from@example.com", to, msg)
	if err != nil {
		log.Fatal(err)
	}
}

Wonderful hack by https://gist.github.com/andelf/5118732

I don't know why Standard library not implementing LOGIN Mechanism.

@ashishtiwari1993 Thank you so much for this! I was going crazy trying to figure it out!!

Enabling "less secure apps" didn't work for me, I kept getting a Error when sending mail: 535 5.7.8 Username and Password not accepted. Learn more at 5.7.8 https://support.google.com/mail/?p=BadCredentials y19sm6477535pfe.9 - gsmtp even though that was definitely my username and password.

What did was turning turning on 2FA and generating an app password instead. The app password can be used in lieu of your actual gmail password anywhere where your password is required.

Thanks brother, this worked for me (replacing password for app password).

Hi @luizuatanabe. The same thing happens to me. Due to Google's policy change in May 2022, it is now no longer possible to disable the "less secure apps" option. Do you know if there is a way to perform this validation to send emails?

@parkare same thing here. Did you figure out a solution?

The "less secure apps" is available for google enterprise accounts.

https://gist.github.com/jpillora/cb46d183eca0710d909a?permalink_comment_id=3519541#gistcomment-3519541

This worked! Instead of password generate a app password and use it as password. Works like charm!!