go-smtp

by emersion

emersion / go-smtp

:outbox_tray: An SMTP client & server library written in Go

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go-smtp

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An ESMTP client and server library written in Go.

Features

  • ESMTP client & server implementing RFC 5321
  • Support for SMTP AUTH and PIPELINING
  • UTF-8 support for subject and message
  • LMTP support

Usage

Client

package main

import ( "log" "strings"

"github.com/emersion/go-sasl"
"github.com/emersion/go-smtp"

)

func main() { // Set up authentication information. auth := sasl.NewPlainClient("", "[email protected]", "password")

// Connect to the server, authenticate, set the sender and recipient,
// and send the email all in one step.
to := []string{"[email protected]"}
msg := strings.NewReader("To: [email protected]\r\n" +
    "Subject: discount Gophers!\r\n" +
    "\r\n" +
    "This is the email body.\r\n")
err := smtp.SendMail("mail.example.com:25", auth, "[email protected]", to, msg)
if err != nil {
    log.Fatal(err)
}

}

If you need more control, you can use

Client
instead.

Server

package main

import ( "errors" "io" "io/ioutil" "log" "time"

"github.com/emersion/go-smtp"

)

// The Backend implements SMTP server methods. type Backend struct{}

// Login handles a login command with username and password. func (bkd *Backend) Login(state *smtp.ConnectionState, username, password string) (smtp.Session, error) { if username != "username" || password != "password" { return nil, errors.New("Invalid username or password") } return &Session{}, nil }

// AnonymousLogin requires clients to authenticate using SMTP AUTH before sending emails func (bkd *Backend) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session, error) { return nil, smtp.ErrAuthRequired }

// A Session is returned after successful login. type Session struct{}

func (s *Session) Mail(from string, opts smtp.MailOptions) error { log.Println("Mail from:", from) return nil }

func (s *Session) Rcpt(to string) error { log.Println("Rcpt to:", to) return nil }

func (s *Session) Data(r io.Reader) error { if b, err := ioutil.ReadAll(r); err != nil { return err } else { log.Println("Data:", string(b)) } return nil }

func (s *Session) Reset() {}

func (s *Session) Logout() error { return nil }

func main() { be := &Backend{}

s := smtp.NewServer(be)

s.Addr = ":1025"
s.Domain = "localhost"
s.ReadTimeout = 10 * time.Second
s.WriteTimeout = 10 * time.Second
s.MaxMessageBytes = 1024 * 1024
s.MaxRecipients = 50
s.AllowInsecureAuth = true

log.Println("Starting server at", s.Addr)
if err := s.ListenAndServe(); err != nil {
    log.Fatal(err)
}

}

You can use the server manually with

telnet
:
$ telnet localhost 1025
EHLO localhost
AUTH PLAIN
AHVzZXJuYW1lAHBhc3N3b3Jk
MAIL FROM:
RCPT TO:
DATA
Hey <3
.

Relationship with net/smtp

The Go standard library provides a SMTP client implementation in

net/smtp
. However
net/smtp
is frozen: it's not getting any new features. go-smtp provides a server implementation and a number of client improvements.

Licence

MIT

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