HOW-TO: send email via SMTP with Go.

smtp-send.go

package main

import (
  "crypto/tls"
  "fmt"
  "log"
  "net"
  "net/mail"
  "net/smtp"
)

func main() {
  // the basics
  from := mail.Address{"senders name", "username@sender.com"}
  to := mail.Address{"recipients name", "username@recipient.com"}
  body := "this is the body line1.\nthis is the body line2.\nthis is the body line3.\n"
  subject := "this is the subject line"

  // setup the remote smtpserver & auth info
  smtpserver := "remote.mailserver.com:25"
  auth := smtp.PlainAuth("", "username@sender.com", "senders-password", "remote.mailserver.com")

  // setup a map for the headers
  header := make(map[string]string)
  header["From"] = from.String()
  header["To"] = to.String()
  header["Subject"] = subject

  // setup the message
  message := ""
  for k, v := range header {
    message += fmt.Sprintf("%s: %s\r\n", k, v)
  }
  message += "\r\n" + body

  // create the smtp connection
  c, err := smtp.Dial(smtpserver)
  if err != nil {
    log.Panic(err)
  }

  // set some TLS options, so we can make sure a non-verified cert won't stop us sending
  host, _, _ := net.SplitHostPort(smtpserver)
  // make a nice tls.Config struct 
  tlc := &tls.Config{
    InsecureSkipVerify: true,
    ServerName:         host,
  }
  // send the tls.Config to StartTLS to generate the STARTTLS
  if err = c.StartTLS(tlc); err != nil {
    log.Panic(err)
  }
  // let's authenticate
  if err = c.Auth(auth); err != nil {
    log.Panic(err)
  }
  // To && From
  if err = c.Mail(from.Address); err != nil {
    log.Panic(err)
  }
  // Recipient
  if err = c.Rcpt(to.Address); err != nil {
    log.Panic(err)
  }
  // Data
  w, err := c.Data()
  if err != nil {
    log.Panic(err)
  }
  // everything is setup; write it 
  _, err = w.Write([]byte(message))
  if err != nil {
    log.Panic(err)
  }
  err = w.Close()
  if err != nil {
    log.Panic(err)
  }
  c.Quit()
}