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 := "[email protected]"
	pass := "..."
	to := "[email protected]"

	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")
}

why sending mail using net/smtp goes to spam?

I get the log error :

smtp error: 535 5.7.8 Username and Password not accepted. Learn more at
5.7.8  https://support.google.com/mail/?p=BadCredentials q15sm14168864pgm.47 - gsmtp

and an email saying: "Someone just used your password to try to sign in to your account from a non-Google app. Google blocked them, but you should check what happened. Review your account activity to make sure no one else has access."

@mileung Just allow access to less secure apps in your gmail.
Ref cited: https://serverfault.com/questions/635139/how-to-fix-send-mail-authorization-failed-534-5-7-14

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.

Although the email is getting sent. Immediately post that program exits with below error. Please suggest solution

Only one usage of each socket address (protocol/network address/port) is normally permitted.

You can test it with https://mailtrap.io

I got this error while using golang,
2015/11/26 15:04:45 smtp error: x509: certificate signed by unknown authority
testing in python show gmail works fine
any suggestion?

That just means the CA that signed the certificate isn't recognized. This is usually the case with selfsigned certificates.

My god you have literally no idea how long I have been trying to solve this one tiny little issue with sending the actual email and this just solved it for me. Thank you so much!

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{"[email protected]"}
	msg := []byte("To: [email protected]\r\n" +
		"Subject: New Hack\r\n" +
		"\r\n" +
		"Wonderful solution\r\n")
	err := smtp.SendMail("smtp.gmail.com:587", auth, "[email protected]", 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.

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 [email protected] so I am seeing [email protected] in the mail list of receiver inbox but I want my custom sender name instead of [email protected],
I am using SMTP plain auth

from:= [email protected]
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{"[email protected]"}
	msg := []byte("To: [email protected]\r\n" +
		"Subject: New Hack\r\n" +
		"\r\n" +
		"Wonderful solution\r\n")
	err := smtp.SendMail("smtp.gmail.com:587", auth, "[email protected]", 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!!

upd: this work for me, need add parametr from in msg object
msg := []byte("From: ***@mail.com\r\n" +
"To: ***@gmail.com\r\n" +
"Subject: New Hack\r\n" +
"\r\n" +
"Wonderful solution\r\n")