Some progress was made:

- Implemented proper AUTH LOGIN mechanism
- Implemented msgWriter for handling io
- Implemented proper mail header formatting/output
- Minor refactoring

auth.go

@@ -15,9 +15,6 @@ const (
 
 	// SMTPAuthCramMD5 is the "CRAM-MD5" SASL authentication mechanism as described in RFC 4954
 	SMTPAuthCramMD5 SMTPAuthType = "CRAM-MD5"
-
-	// SMTPAuthDigestMD5 is the "DIGEST-MD5" SASL authentication mechanism as described in RFC 4954
-	SMTPAuthDigestMD5 SMTPAuthType = "DIGEST-MD5"
 )
 
 // SMTP Auth related static errors
@@ -30,7 +27,4 @@ var (
 
 	// ErrCramMD5AuthNotSupported should be used if the target server does not support the "CRAM-MD5" schema
 	ErrCramMD5AuthNotSupported = errors.New("server does not support SMTP AUTH type: CRAM-MD5")
-
-	// ErrDigestMD5AuthNotSupported should be used if the target server does not support the "DIGEST-MD5" schema
-	ErrDigestMD5AuthNotSupported = errors.New("server does not support SMTP AUTH type: DIGEST-MD5")
 )

auth/login.go

@@ -0,0 +1,69 @@
+// Package auth implements the LOGIN and MD5-DIGEST smtp authentication mechansims
+package auth
+
+import (
+	"errors"
+	"fmt"
+	"net/smtp"
+)
+
+type loginAuth struct {
+	username, password string
+	host               string
+}
+
+const (
+	// ServerRespUsername represents the "Username:" response by the SMTP server
+	ServerRespUsername = "Username:"
+
+	// ServerRespPassword represents the "Password:" response by the SMTP server
+	ServerRespPassword = "Password:"
+)
+
+// LoginAuth returns an Auth that implements the LOGIN authentication
+// mechanism as it is used by MS Outlook. The Auth works similar to PLAIN
+// but instead of sending all in one response, the login is handled within
+// 3 steps:
+// - Sending AUTH LOGIN (server responds with "Username:")
+// - Sending the username (server responds with "Password:")
+// - Sending the password (server authenticates)
+//
+// LoginAuth will only send the credentials if the connection is using TLS
+// or is connected to localhost. Otherwise authentication will fail with an
+// error, without sending the credentials.
+func LoginAuth(username, password, host string) smtp.Auth {
+	return &loginAuth{username, password, host}
+}
+
+func isLocalhost(name string) bool {
+	return name == "localhost" || name == "127.0.0.1" || name == "::1"
+}
+
+func (a *loginAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
+	// Must have TLS, or else localhost server.
+	// Note: If TLS is not true, then we can't trust ANYTHING in ServerInfo.
+	// In particular, it doesn't matter if the server advertises LOGIN auth.
+	// That might just be the attacker saying
+	// "it's ok, you can trust me with your password."
+	if !server.TLS && !isLocalhost(server.Name) {
+		return "", nil, errors.New("unencrypted connection")
+	}
+	if server.Name != a.host {
+		return "", nil, errors.New("wrong host name")
+	}
+	return "LOGIN", nil, nil
+}
+
+func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
+	if more {
+		switch string(fromServer) {
+		case ServerRespUsername:
+			return []byte(a.username), nil
+		case ServerRespPassword:
+			return []byte(a.password), nil
+		default:
+			return nil, fmt.Errorf("unexpected server response: %s", string(fromServer))
+		}
+	}
+	return nil, nil
+}

client.go

@@ -5,6 +5,7 @@ import (
 	"crypto/tls"
 	"errors"
 	"fmt"
+	"github.com/wneessen/go-mail/auth"
 	"net"
 	"net/smtp"
 	"os"
@@ -275,10 +276,54 @@ func (c *Client) DialWithContext(pc context.Context) error {
 }
 
 // Send sends out the mail message
-func (c *Client) Send() error {
+func (c *Client) Send(ml ...*Msg) error {
 	if err := c.checkConn(); err != nil {
 		return fmt.Errorf("failed to send mail: %w", err)
 	}
+	for _, m := range ml {
+		f, err := m.GetSender(false)
+		if err != nil {
+			return err
+		}
+		rl, err := m.GetRecipients()
+		if err != nil {
+			return err
+		}
+
+		if err := c.sc.Mail(f); err != nil {
+			return fmt.Errorf("sending MAIL FROM command failed: %w", err)
+		}
+		for _, r := range rl {
+			if err := c.sc.Rcpt(r); err != nil {
+				return fmt.Errorf("sending RCPT TO command failed: %w", err)
+			}
+		}
+		w := os.Stderr
+
+		/*
+			w, err := c.sc.Data()
+			if err != nil {
+				return fmt.Errorf("sending DATA command failed: %w", err)
+			}
+
+		*/
+
+		_, err = m.Write(w)
+		if err != nil {
+			return fmt.Errorf("sending mail content failed: %w", err)
+		}
+
+		if err := w.Close(); err != nil {
+			return fmt.Errorf("failed to close DATA writer: %w", err)
+		}
+
+		if err := c.Reset(); err != nil {
+			return fmt.Errorf("sending RSET command failed: %s", err)
+		}
+		if err := c.checkConn(); err != nil {
+			return fmt.Errorf("failed to check server connection: %w", err)
+		}
+	}
 
 	return nil
 }
@@ -288,7 +333,7 @@ func (c *Client) Close() error {
 	if err := c.checkConn(); err != nil {
 		return err
 	}
-	if err := c.sc.Close(); err != nil {
+	if err := c.sc.Quit(); err != nil {
 		return fmt.Errorf("failed to close SMTP client: %w", err)
 	}
 
@@ -309,14 +354,17 @@ func (c *Client) Reset() error {
 
 // DialAndSend establishes a connection to the SMTP server with a
 // default context.Background and sends the mail
-func (c *Client) DialAndSend() error {
+func (c *Client) DialAndSend(ml ...*Msg) error {
 	ctx := context.Background()
 	if err := c.DialWithContext(ctx); err != nil {
 		return fmt.Errorf("dial failed: %w", err)
 	}
-	if err := c.Send(); err != nil {
+	if err := c.Send(ml...); err != nil {
 		return fmt.Errorf("send failed: %w", err)
 	}
+	if err := c.Close(); err != nil {
+		return fmt.Errorf("failed to close connction: %s", err)
+	}
 	return nil
 }
 
@@ -383,17 +431,12 @@ func (c *Client) auth() error {
 			if !strings.Contains(sat, string(SMTPAuthLogin)) {
 				return ErrLoginAuthNotSupported
 			}
-			c.sa = smtp.PlainAuth("", c.user, c.pass, c.host)
+			c.sa = auth.LoginAuth(c.user, c.pass, c.host)
 		case SMTPAuthCramMD5:
 			if !strings.Contains(sat, string(SMTPAuthCramMD5)) {
 				return ErrCramMD5AuthNotSupported
 			}
 			c.sa = smtp.CRAMMD5Auth(c.user, c.pass)
-		case SMTPAuthDigestMD5:
-			if !strings.Contains(sat, string(SMTPAuthDigestMD5)) {
-				return ErrDigestMD5AuthNotSupported
-			}
-			c.sa = smtp.CRAMMD5Auth(c.user, c.pass)
 		default:
 			return fmt.Errorf("unsupported SMTP AUTH type %q", c.satype)
 		}

cmd/main.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"github.com/wneessen/go-mail"
 	"os"
-	"time"
 )
 
 func main() {
@@ -16,42 +15,36 @@ func main() {
 	tu := os.Getenv("TEST_USER")
 	tp := os.Getenv("TEST_PASS")
 
+	fa := "Winni Neessen <wn@neessen.cloud>"
+	toa := "Winfried Neessen <wn@neessen.net>"
+	//toa = "Winfried Neessen <wneessen@arch-vm.fritz.box>"
+
 	m := mail.NewMsg()
-	if err := m.From(`Winni Neessen <wn@neessen.net>`); err != nil {
+	if err := m.From(fa); err != nil {
 		fmt.Printf("failed to set FROM addres: %s", err)
 		os.Exit(1)
 	}
-	if err := m.To("t1+2941@test.de", "foo@bar.de", "blubb@blah.com"); err != nil {
+	if err := m.To(toa); err != nil {
 		fmt.Printf("failed to set TO address: %s", err)
 		os.Exit(1)
 	}
-	m.CcIgnoreInvalid("cc@test.de", "bar.de", "cc@blah.com")
-	m.BccIgnoreInvalid("bcc@test.de", "bcc@blah.com")
 	m.Subject("This is the Subject with Umlauts: üöäß")
-	m.SetHeader(mail.HeaderContentLang, "en")
+	m.SetHeader(mail.HeaderContentLang, "de", "en", "fr", "sp", "de", "en", "fr", "sp", "de", "en", "fr",
+		"sp", "de", "en", "fr", "sp")
+	m.SetHeader(mail.HeaderListUnsubscribePost, "üüüüüüüü", "aaaaääää", "ßßßßßßßßß", "XXXXXX", "ZZZZZ", "XXXXXXXX",
+		"äää äää", "YYYYYY", "XXXXXX", "ZZZZZ", "üäö´")
 	m.SetMessageID()
 	m.SetDate()
 	m.SetBulk()
-	m.Header()
 
-	c, err := mail.NewClient(th, mail.WithTimeout(time.Millisecond*500), mail.WithTLSPolicy(mail.TLSMandatory),
-		mail.WithSMTPAuth(mail.SMTPAuthDigestMD5), mail.WithUsername(tu), mail.WithPassword(tp))
+	c, err := mail.NewClient(th, mail.WithTLSPolicy(mail.TLSMandatory),
+		mail.WithSMTPAuth(mail.SMTPAuthLogin), mail.WithUsername(tu),
+		mail.WithPassword(tp))
 	if err != nil {
 		fmt.Printf("failed to create new client: %s\n", err)
 		os.Exit(1)
 	}
-	defer func() {
-		if err := c.Reset(); err != nil {
-			fmt.Printf("failed to reset: %s\n", err)
-			os.Exit(1)
-		}
-		if err := c.Close(); err != nil {
-			fmt.Printf("failed to close: %s\n", err)
-			os.Exit(1)
-		}
-	}()
-
-	if err := c.DialAndSend(); err != nil {
+	if err := c.DialAndSend(m); err != nil {
 		fmt.Printf("failed to dial: %s\n", err)
 		os.Exit(1)
 	}

msg.go

@@ -1,7 +1,9 @@
 package mail
 
 import (
+	"errors"
 	"fmt"
+	"io"
 	"math/rand"
 	"mime"
 	"net/mail"
@@ -9,6 +11,14 @@ import (
 	"time"
 )
 
+var (
+	// ErrNoFromAddress should be used when a FROM address is requrested but not set
+	ErrNoFromAddress = errors.New("no FROM address set")
+
+	// ErrNoRcptAddresses should be used when the list of RCPTs is empty
+	ErrNoRcptAddresses = errors.New("no recipient addresses set")
+)
+
 // Msg is the mail message struct
 type Msg struct {
 	// charset represents the charset of the mail (defaults to UTF-8)
@@ -167,7 +177,7 @@ func (m *Msg) SetMessageID() {
 	if err != nil {
 		hn = "localhost.localdomain"
 	}
-	ct := time.Now().UnixMicro()
+	ct := time.Now().Unix()
 	r := rand.New(rand.NewSource(ct))
 	rn := r.Int()
 	pid := os.Getpid()
@@ -194,18 +204,40 @@ func (m *Msg) SetDate() {
 	m.SetHeader(HeaderDate, ts)
 }
 
-// Header does something
-// FIXME: This is only here to quickly show the set headers for debugging purpose. Remove me later
-func (m *Msg) Header() {
-	fmt.Println("Address header:")
-	for k, v := range m.addrHeader {
-		fmt.Printf(" - %s: %s\n", k, v)
+// GetSender returns the currently set FROM address. If f is true, it will return the full
+// address string including the address name, if set
+func (m *Msg) GetSender(ff bool) (string, error) {
+	f, ok := m.addrHeader[HeaderFrom]
+	if !ok || len(f) == 0 {
+		return "", ErrNoFromAddress
 	}
-	fmt.Println("\nGeneric header:")
-	for k, v := range m.genHeader {
-		fmt.Printf(" - %s: %s\n", k, v)
+	if ff {
+		return f[0].String(), nil
 	}
-	fmt.Println()
+	return f[0].Address, nil
+}
+
+// GetRecipients returns a list of the currently set TO/CC/BCC addresses.
+func (m *Msg) GetRecipients() ([]string, error) {
+	var rl []string
+	for _, t := range []AddrHeader{HeaderTo, HeaderCc, HeaderBcc} {
+		al, ok := m.addrHeader[t]
+		if !ok || len(al) == 0 {
+			continue
+		}
+		for _, r := range al {
+			rl = append(rl, r.Address)
+		}
+	}
+	if len(rl) <= 0 {
+		return rl, ErrNoRcptAddresses
+	}
+	return rl, nil
+}
+func (m *Msg) Write(w io.Writer) (int64, error) {
+	mw := &msgWriter{w: w}
+	mw.writeMsg(m)
+	return mw.n, mw.err
 }
 
 // setEncoder creates a new mime.WordEncoder based on the encoding setting of the message

msgwriter.go

@@ -0,0 +1,96 @@
+package mail
+
+import (
+	"io"
+	"strings"
+)
+
+// MaxHeaderLength defines the maximum line length for a mail header
+// RFC 2047 suggests 76 characters
+const MaxHeaderLength = 76
+
+// msgWriter handles the I/O to the io.WriteCloser of the SMTP client
+type msgWriter struct {
+	w io.Writer
+	n int64
+	//writers    [3]*multipart.Writer
+	//partWriter io.Writer
+	//depth      uint8
+	err error
+}
+
+// writeMsg formats the message and sends it to its io.Writer
+func (mw *msgWriter) writeMsg(m *Msg) {
+	if _, ok := m.genHeader["Date"]; !ok {
+		m.SetDate()
+	}
+	for k, v := range m.genHeader {
+		mw.writeHeader(k, v...)
+	}
+	for _, t := range []AddrHeader{HeaderFrom, HeaderTo, HeaderCc} {
+		if al, ok := m.addrHeader[t]; ok {
+			var v []string
+			for _, a := range al {
+				v = append(v, a.String())
+			}
+			mw.writeHeader(Header(t), v...)
+		}
+	}
+	mw.writeString("\r\n")
+	mw.writeString("This is a test mail")
+}
+
+// writeHeader writes a header into the msgWriter's io.Writer
+func (mw *msgWriter) writeHeader(k Header, v ...string) {
+	mw.writeString(string(k))
+	if len(v) == 0 {
+		mw.writeString(":\r\n")
+		return
+	}
+	mw.writeString(": ")
+
+	// Chars left: MaxHeaderLength - "<Headername>: " - "CRLF"
+	cl := MaxHeaderLength - len(k) - 4
+	for i, s := range v {
+		nfl := 0
+		if i < len(v) {
+			nfl = len(v[i])
+		}
+		if cl-len(s) < 1 {
+			if p := strings.IndexByte(s, ' '); p != -1 {
+				mw.writeString(s[:p])
+				mw.writeString("\r\n ")
+				mw.writeString(s[p:])
+				cl -= len(s[p:])
+				continue
+			}
+		}
+		if cl < 1 || cl-nfl < 1 {
+			mw.writeString("\r\n")
+			cl = MaxHeaderLength - 4
+			if i != len(v) {
+				mw.writeString(" ")
+				cl -= 1
+			}
+		}
+		mw.writeString(s)
+		cl -= len(s)
+
+		if i != len(v)-1 {
+			mw.writeString(", ")
+			cl -= 2
+		}
+
+	}
+	mw.writeString("\r\n")
+}
+
+// writeString writes a string into the msgWriter's io.Writer interface
+func (mw *msgWriter) writeString(s string) {
+	if mw.err != nil {
+		return
+	}
+	var n int
+	n, mw.err = io.WriteString(mw.w, s)
+	mw.n += int64(n)
+}