// Copyright 2010 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. // Package smtp implements the Simple Mail Transfer Protocol as defined in RFC 5321. // It also implements the following extensions: // 8BITMIME RFC 1652 // AUTH RFC 2554 // STARTTLS RFC 3207 // Additional extensions may be handled by clients. // // The smtp package is frozen and is not accepting new features. // Some external packages provide more functionality. See: // // https://godoc.org/?q=smtp package smtp import ( "crypto/tls" "encoding/base64" "errors" "fmt" "io" "net" "net/textproto" "strings" ) // A Client represents a client connection to an SMTP server. type Client struct { // Text is the textproto.Conn used by the Client. It is exported to allow for // clients to add extensions. Text *textproto.Conn // keep a reference to the connection so it can be used to create a TLS // connection later conn net.Conn // whether the Client is using TLS tls bool serverName string // map of supported extensions ext map[string]string // supported auth mechanisms auth []string localName string // the name to use in HELO/EHLO didHello bool // whether we've said HELO/EHLO helloError error // the error from the hello } // Dial returns a new Client connected to an SMTP server at addr. // The addr must include a port, as in "mail.example.com:smtp". func Dial(addr string) (*Client, error) { conn, err := net.Dial("tcp", addr) if err != nil { return nil, err } host, _, _ := net.SplitHostPort(addr) return NewClient(conn, host) } // NewClient returns a new Client using an existing connection and host as a // server name to be used when authenticating. func NewClient(conn net.Conn, host string) (*Client, error) { text := textproto.NewConn(conn) _, _, err := text.ReadResponse(220) if err != nil { text.Close() return nil, err } c := &Client{Text: text, conn: conn, serverName: host, localName: "localhost"} _, c.tls = conn.(*tls.Conn) return c, nil } // Close closes the connection. func (c *Client) Close() error { return c.Text.Close() } // hello runs a hello exchange if needed. func (c *Client) hello() error { if !c.didHello { c.didHello = true err := c.ehlo() if err != nil { c.helloError = c.helo() } } return c.helloError } // Hello sends a HELO or EHLO to the server as the given host name. // Calling this method is only necessary if the client needs control // over the host name used. The client will introduce itself as "localhost" // automatically otherwise. If Hello is called, it must be called before // any of the other methods. func (c *Client) Hello(localName string) error { if err := validateLine(localName); err != nil { return err } if c.didHello { return errors.New("smtp: Hello called after other methods") } c.localName = localName return c.hello() } // cmd is a convenience function that sends a command and returns the response func (c *Client) cmd(expectCode int, format string, args ...interface{}) (int, string, error) { id, err := c.Text.Cmd(format, args...) if err != nil { return 0, "", err } c.Text.StartResponse(id) defer c.Text.EndResponse(id) code, msg, err := c.Text.ReadResponse(expectCode) return code, msg, err } // helo sends the HELO greeting to the server. It should be used only when the // server does not support ehlo. func (c *Client) helo() error { c.ext = nil _, _, err := c.cmd(250, "HELO %s", c.localName) return err } // ehlo sends the EHLO (extended hello) greeting to the server. It // should be the preferred greeting for servers that support it. func (c *Client) ehlo() error { _, msg, err := c.cmd(250, "EHLO %s", c.localName) if err != nil { return err } ext := make(map[string]string) extList := strings.Split(msg, "\n") if len(extList) > 1 { extList = extList[1:] for _, line := range extList { args := strings.SplitN(line, " ", 2) if len(args) > 1 { ext[args[0]] = args[1] } else { ext[args[0]] = "" } } } if mechs, ok := ext["AUTH"]; ok { c.auth = strings.Split(mechs, " ") } c.ext = ext return err } // StartTLS sends the STARTTLS command and encrypts all further communication. // Only servers that advertise the STARTTLS extension support this function. func (c *Client) StartTLS(config *tls.Config) error { if err := c.hello(); err != nil { return err } _, _, err := c.cmd(220, "STARTTLS") if err != nil { return err } c.conn = tls.Client(c.conn, config) c.Text = textproto.NewConn(c.conn) c.tls = true return c.ehlo() } // TLSConnectionState returns the client's TLS connection state. // The return values are their zero values if StartTLS did // not succeed. func (c *Client) TLSConnectionState() (state tls.ConnectionState, ok bool) { tc, ok := c.conn.(*tls.Conn) if !ok { return } return tc.ConnectionState(), true } // Verify checks the validity of an email address on the server. // If Verify returns nil, the address is valid. A non-nil return // does not necessarily indicate an invalid address. Many servers // will not verify addresses for security reasons. func (c *Client) Verify(addr string) error { if err := validateLine(addr); err != nil { return err } if err := c.hello(); err != nil { return err } _, _, err := c.cmd(250, "VRFY %s", addr) return err } // Auth authenticates a client using the provided authentication mechanism. // A failed authentication closes the connection. // Only servers that advertise the AUTH extension support this function. func (c *Client) Auth(a Auth) error { if err := c.hello(); err != nil { return err } encoding := base64.StdEncoding mech, resp, err := a.Start(&ServerInfo{c.serverName, c.tls, c.auth}) if err != nil { c.Quit() return err } resp64 := make([]byte, encoding.EncodedLen(len(resp))) encoding.Encode(resp64, resp) code, msg64, err := c.cmd(0, strings.TrimSpace(fmt.Sprintf("AUTH %s %s", mech, resp64))) for err == nil { var msg []byte switch code { case 334: msg, err = encoding.DecodeString(msg64) case 235: // the last message isn't base64 because it isn't a challenge msg = []byte(msg64) default: err = &textproto.Error{Code: code, Msg: msg64} } if err == nil { resp, err = a.Next(msg, code == 334) } if err != nil { // abort the AUTH c.cmd(501, "*") c.Quit() break } if resp == nil { break } resp64 = make([]byte, encoding.EncodedLen(len(resp))) encoding.Encode(resp64, resp) code, msg64, err = c.cmd(0, string(resp64)) } return err } // Mail issues a MAIL command to the server using the provided email address. // If the server supports the 8BITMIME extension, Mail adds the BODY=8BITMIME // parameter. If the server supports the SMTPUTF8 extension, Mail adds the // SMTPUTF8 parameter. // This initiates a mail transaction and is followed by one or more Rcpt calls. func (c *Client) Mail(from string) error { if err := validateLine(from); err != nil { return err } if err := c.hello(); err != nil { return err } cmdStr := "MAIL FROM:<%s>" if c.ext != nil { if _, ok := c.ext["8BITMIME"]; ok { cmdStr += " BODY=8BITMIME" } if _, ok := c.ext["SMTPUTF8"]; ok { cmdStr += " SMTPUTF8" } } _, _, err := c.cmd(250, cmdStr, from) return err } // Rcpt issues a RCPT command to the server using the provided email address. // A call to Rcpt must be preceded by a call to Mail and may be followed by // a Data call or another Rcpt call. func (c *Client) Rcpt(to string) error { if err := validateLine(to); err != nil { return err } _, _, err := c.cmd(25, "RCPT TO:<%s>", to) return err } type dataCloser struct { c *Client io.WriteCloser } func (d *dataCloser) Close() error { d.WriteCloser.Close() _, _, err := d.c.Text.ReadResponse(250) return err } // Data issues a DATA command to the server and returns a writer that // can be used to write the mail headers and body. The caller should // close the writer before calling any more methods on c. A call to // Data must be preceded by one or more calls to Rcpt. func (c *Client) Data() (io.WriteCloser, error) { _, _, err := c.cmd(354, "DATA") if err != nil { return nil, err } return &dataCloser{c, c.Text.DotWriter()}, nil } var testHookStartTLS func(*tls.Config) // nil, except for tests // SendMail connects to the server at addr, switches to TLS if // possible, authenticates with the optional mechanism a if possible, // and then sends an email from address from, to addresses to, with // message msg. // The addr must include a port, as in "mail.example.com:smtp". // // The addresses in the to parameter are the SMTP RCPT addresses. // // The msg parameter should be an RFC 822-style email with headers // first, a blank line, and then the message body. The lines of msg // should be CRLF terminated. The msg headers should usually include // fields such as "From", "To", "Subject", and "Cc". Sending "Bcc" // messages is accomplished by including an email address in the to // parameter but not including it in the msg headers. // // The SendMail function and the net/smtp package are low-level // mechanisms and provide no support for DKIM signing, MIME // attachments (see the mime/multipart package), or other mail // functionality. Higher-level packages exist outside of the standard // library. func SendMail(addr string, a Auth, from string, to []string, msg []byte) error { if err := validateLine(from); err != nil { return err } for _, recp := range to { if err := validateLine(recp); err != nil { return err } } c, err := Dial(addr) if err != nil { return err } defer c.Close() if err = c.hello(); err != nil { return err } if ok, _ := c.Extension("STARTTLS"); ok { config := &tls.Config{ServerName: c.serverName} if testHookStartTLS != nil { testHookStartTLS(config) } if err = c.StartTLS(config); err != nil { return err } } if a != nil && c.ext != nil { if _, ok := c.ext["AUTH"]; !ok { return errors.New("smtp: server doesn't support AUTH") } if err = c.Auth(a); err != nil { return err } } if err = c.Mail(from); err != nil { return err } for _, addr := range to { if err = c.Rcpt(addr); err != nil { return err } } w, err := c.Data() if err != nil { return err } _, err = w.Write(msg) if err != nil { return err } err = w.Close() if err != nil { return err } return c.Quit() } // Extension reports whether an extension is support by the server. // The extension name is case-insensitive. If the extension is supported, // Extension also returns a string that contains any parameters the // server specifies for the extension. func (c *Client) Extension(ext string) (bool, string) { if err := c.hello(); err != nil { return false, "" } if c.ext == nil { return false, "" } ext = strings.ToUpper(ext) param, ok := c.ext[ext] return ok, param } // Reset sends the RSET command to the server, aborting the current mail // transaction. func (c *Client) Reset() error { if err := c.hello(); err != nil { return err } _, _, err := c.cmd(250, "RSET") return err } // Noop sends the NOOP command to the server. It does nothing but check // that the connection to the server is okay. func (c *Client) Noop() error { if err := c.hello(); err != nil { return err } _, _, err := c.cmd(250, "NOOP") return err } // Quit sends the QUIT command and closes the connection to the server. func (c *Client) Quit() error { if err := c.hello(); err != nil { return err } _, _, err := c.cmd(221, "QUIT") if err != nil { return err } return c.Text.Close() } // validateLine checks to see if a line has CR or LF as per RFC 5321 func validateLine(line string) error { if strings.ContainsAny(line, "\n\r") { return errors.New("smtp: A line must not contain CR or LF") } return nil }