Send email over socks proxy on golang

gistfile1.txt

package main

import (
	"crypto/tls"
	"fmt"
	"io"
	"log"
	"net"
	"net/mail"
	"time"

	"net/smtp"

	"golang.org/x/net/proxy"
)

func main() {

	from := mail.Address{Address: "mail from"}
	to := mail.Address{Address: "mail to"}
	subj := "This is the email subject"
	body := "This is an example body.\n With two lines."

	serverName := "smtp.mail.ru:465"
	proxyAddr := "0.0.0.0:3000"
	auth := smtp.PlainAuth("", "user", "password", serverName)

	proxyAuth := proxy.Auth{
		User:     "admin",
		Password: "123456",
	}

	baseDialer := &net.Dialer{
		Timeout:   3 * time.Second,
		KeepAlive: 3 * time.Second,
	}

	dialer, err := proxy.SOCKS5("tcp", proxyAddr, &proxyAuth, baseDialer)
	if err != nil {
		log.Fatal(err)
	}

	var cn net.Conn
	if cn, err = dialer.Dial("tcp", serverName); err != nil {
		log.Fatal(err)
	}

	conf := &tls.Config{
		ServerName:         serverName,
		InsecureSkipVerify: true,
	}

	tlsConn := tls.Client(cn, conf)

	var cl *smtp.Client
	if cl, err = smtp.NewClient(tlsConn, serverName); err != nil {
		log.Fatal(err)
	}

	defer cl.Close()
	defer cl.Quit()

	if err = cl.Hello("localhost"); err != nil {
		log.Fatal(err)
	}

	if err = cl.Auth(auth); err != nil {
		log.Fatal(err)
	}

	if err = cl.Mail(from.Address); err != nil {
		log.Fatal(err)
	}

	if err = cl.Rcpt(to.Address); err != nil {
		log.Fatal(err)
	}

	var w io.WriteCloser
	if w, err = cl.Data(); err != nil {
		log.Fatal(err)
	}

	headers := make(map[string]string)

	headers["From"] = from.String()
	headers["To"] = to.String()
	headers["Subject"] = subj

	msg := ""
	for k, v := range headers {
		msg += fmt.Sprintf("%s: %s\r\n", k, v)
	}

	msg += fmt.Sprintf("\r\n" + body)

	if _, err = w.Write([]byte(msg)); err != nil {
		log.Fatal(err)
	}

	if err = w.Close(); err != nil {
		log.Fatal(err)
	}

	log.Println("Ok, exit.")
}