smtpd

README

Go smtpd

Package smtpd implements an SMTP server in golang.

Features

• STARTTLS (using crypto/tls)
• Authentication (PLAIN/LOGIN, only after STARTTLS)
• XCLIENT and PROXY protocol (for running behind a proxy)
• Connection, HELO, sender and recipient checks for rejecting e-mails using callbacks
• Configurable limits for: connection count, message size and recipient count
• Hands incoming e-mail off to a configured callback function

Version numbers

The package is tagged with semantic version numbers, making it suitable for use in a Go Module.

Feedback

If you end up using this package or have any feedback, I'd very much like to hear about it. You can reach me by email.

Documentation

Overview

Package smtpd implements an SMTP server with support for STARTTLS, authentication (PLAIN/LOGIN), XCLIENT and optional restrictions on the different stages of the SMTP session.

Index

• type Envelope
  • func (env *Envelope) AddReceivedLine(peer Peer)
• type Error
  • func (e Error) Error() string
• type Peer
• type Protocol
• type Server
  • func (srv *Server) ListenAndServe(addr string) error
  • func (srv *Server) Serve(l net.Listener) error

Examples

• Server

Types

type Envelope

type Envelope struct {
	Sender     string
	Recipients []string
	Data       []byte
}

Envelope holds a message

func (*Envelope) AddReceivedLine

func (env *Envelope) AddReceivedLine(peer Peer)

AddReceivedLine prepends a Received header to the Data

type Error

type Error struct {
	Code    int    // The integer error code
	Message string // The error message
}

Error represents an Error reported in the SMTP session.

func (Error) Error

func (e Error) Error() string

Error returns a string representation of the SMTP error

type Peer

type Peer struct {
	HeloName   string               // Server name used in HELO/EHLO command
	Username   string               // Username from authentication, if authenticated
	Password   string               // Password from authentication, if authenticated
	Protocol   Protocol             // Protocol used, SMTP or ESMTP
	ServerName string               // A copy of Server.Hostname
	Addr       net.Addr             // Network address
	TLS        *tls.ConnectionState // TLS Connection details, if on TLS
}

Peer represents the client connecting to the server

type Protocol

type Protocol string

Protocol represents the protocol used in the SMTP session

const (
	// SMTP
	SMTP Protocol = "SMTP"

	// Extended SMTP
	ESMTP = "ESMTP"
)

type Server

type Server struct {
	Hostname       string // Server hostname. (default: "localhost.localdomain")
	WelcomeMessage string // Initial server banner. (default: "<hostname> ESMTP ready.")

	ReadTimeout  time.Duration // Socket timeout for read operations. (default: 60s)
	WriteTimeout time.Duration // Socket timeout for write operations. (default: 60s)
	DataTimeout  time.Duration // Socket timeout for DATA command (default: 5m)

	MaxConnections int // Max concurrent connections, use -1 to disable. (default: 100)
	MaxMessageSize int // Max message size in bytes. (default: 10240000)
	MaxRecipients  int // Max RCPT TO calls for each envelope. (default: 100)

	// New e-mails are handed off to this function.
	// Can be left empty for a NOOP server.
	// If an error is returned, it will be reported in the SMTP session.
	Handler func(peer Peer, env Envelope) error

	DataWriter func(peer Peer) ([]byte, io.WriteCloser, error)

	// Enable various checks during the SMTP session.
	// Can be left empty for no restrictions.
	// If an error is returned, it will be reported in the SMTP session.
	// Use the Error struct for access to error codes.
	ConnectionChecker func(peer Peer) error              // Called upon new connection.
	HeloChecker       func(peer Peer, name string) error // Called after HELO/EHLO.
	SenderChecker     func(peer Peer, addr string) error // Called after MAIL FROM.
	RecipientChecker  func(peer Peer, addr string) error // Called after each RCPT TO.

	// Enable PLAIN/LOGIN authentication, only available after STARTTLS.
	// Can be left empty for no authentication support.
	Authenticator func(peer Peer, username, password string) error

	EnableXCLIENT       bool // Enable XCLIENT support (default: false)
	EnableProxyProtocol bool // Enable proxy protocol support (default: false)

	TLSConfig *tls.Config // Enable STARTTLS support.
	ForceTLS  bool        // Force STARTTLS usage.

	ProtocolLogger *log.Logger
}

Server defines the parameters for running the SMTP server

Example

package main

import (
	"errors"
	"net/smtp"
	"strings"

	"github.com/Supme/smtpd"
)

func main() {
	var server *smtpd.Server

	// No-op server. Accepts and discards
	server = &smtpd.Server{}
	server.ListenAndServe("127.0.0.1:10025")

	// Relay server. Accepts only from single IP address and forwards using the Gmail smtp
	server = &smtpd.Server{

		HeloChecker: func(peer smtpd.Peer, name string) error {
			if !strings.HasPrefix(peer.Addr.String(), "42.42.42.42:") {
				return errors.New("Denied")
			}
			return nil
		},

		Handler: func(peer smtpd.Peer, env smtpd.Envelope) error {

			return smtp.SendMail(
				"smtp.gmail.com:587",
				smtp.PlainAuth(
					"",
					"username@gmail.com",
					"password",
					"smtp.gmail.com",
				),
				env.Sender,
				env.Recipients,
				env.Data,
			)

		},
	}

	server.ListenAndServe("127.0.0.1:10025")
}

func (*Server) ListenAndServe

func (srv *Server) ListenAndServe(addr string) error

ListenAndServe starts the SMTP server and listens on the address provided

func (*Server) Serve

func (srv *Server) Serve(l net.Listener) error

Serve starts the SMTP server and listens on the Listener provided