go-smtp
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("", "user@example.com", "password")
// Connect to the server, authenticate, set the sender and recipient,
// and send the email all in one step.
to := []string{"recipient@example.net"}
msg := strings.NewReader("To: recipient@example.net\r\n" +
"Subject: discount Gophers!\r\n" +
"\r\n" +
"This is the email body.\r\n")
err := smtp.SendMail("mail.example.com:25", auth, "sender@example.org", 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:<root@nsa.gov>
RCPT TO:<root@gchq.gov.uk>
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