Fix the broken SMTP sending

examples/main.go

@@ -22,10 +22,9 @@ var DatabaseBackend = smtp.DatabaseBackend{
 
 // AuthenticationBackend is a smtp.AuthenticationBackend implementation that always returns a fixed address for Authenticate.
 var AuthenticationBackend = smtp.AuthenticationBackend{
-	Authenticate: func(initial string, conn *textproto.Conn) (*smtp.Address, error) {
+	Authenticate: func(initial string, conn *textproto.Conn) (smtp.CheckAddress, error) {
-		return &smtp.Address{
+		return func(address *smtp.Address) (bool, error) {
-			Name:    "test",
+			return true, nil
-			Address: "example.org",
 		}, nil
 	},
 }

smtp.go

@@ -58,9 +58,12 @@ type DatabaseBackend struct {
 
 // AuthenticationBackend is a struct that represents an authentication backend
 type AuthenticationBackend struct {
-	Authenticate func(initial string, conn *textproto.Conn) (*Address, error)
+	Authenticate        func(initial string, conn *textproto.Conn) (CheckAddress, error)
+	SupportedMechanisms []string
 }
 
+type CheckAddress func(*Address) (bool, error)
+
 func readMultilineCodeResponse(conn *textproto.Conn) (int, string, error) {
 	var lines strings.Builder
 	for {
@@ -147,7 +150,7 @@ func speakMultiLine(conn *textproto.Conn, lines []string) error {
 type Receiver struct {
 	underlyingListener net.Listener
 	hostname           string
-	ownedDomains       map[string]any
+	ownedDomains       map[string]struct{}
 	enforceTLS         bool
 	tlsConfig          *tls.Config
 	database           DatabaseBackend
@@ -156,9 +159,9 @@ type Receiver struct {
 
 // NewReceiver creates a new Receiver
 func NewReceiver(conn net.Listener, hostname string, ownedDomains []string, enforceTLS bool, database DatabaseBackend, authentication AuthenticationBackend, tlsConfig *tls.Config) *Receiver {
-	var ownedDomainsMap = make(map[string]any)
+	var ownedDomainsMap = make(map[string]struct{})
 	for _, domain := range ownedDomains {
-		ownedDomainsMap[domain] = nil
+		ownedDomainsMap[domain] = struct{}{}
 	}
 	return &Receiver{
 		underlyingListener: conn,
@@ -191,7 +194,7 @@ func (fr *Receiver) Serve() error {
 func (fr *Receiver) handleConnection(conn net.Conn) {
 	var state struct {
 		HELO bool
-		AUTH *Address
+		AUTH CheckAddress
 		TLS  bool
 		FROM *Address
 		RCPT []*Address
@@ -209,8 +212,6 @@ func (fr *Receiver) handleConnection(conn net.Conn) {
 		return
 	}
 
-	fmt.Println("Connection from", conn.RemoteAddr().String())
-
 	for {
 		line, err := textProto.ReadLine()
 		if err != nil {
@@ -281,6 +282,9 @@ func (fr *Receiver) handleConnection(conn net.Conn) {
 				if fr.enforceTLS {
 					capabilities = append(capabilities, "250-REQUIRETLS")
 				}
+				if fr.auth.SupportedMechanisms != nil {
+					capabilities = append(capabilities, "250-AUTH "+strings.Join(fr.auth.SupportedMechanisms, " "))
+				}
 				capabilities = append(capabilities, defaultCapabilities...)
 				state.HELO = true
 				err = speakMultiLine(textProto, capabilities)
@@ -320,14 +324,14 @@ func (fr *Receiver) handleConnection(conn net.Conn) {
 				}
 				continue
 			} else {
-				address, err := fr.auth.Authenticate(strings.TrimPrefix(line, "AUTH "), textProto)
+				checkAddress, err := fr.auth.Authenticate(strings.TrimPrefix(line, "AUTH "), textProto)
 				if err != nil {
-					_ = textProto.PrintfLine("421 4.7.0 Temporary server error")
+					_ = textProto.PrintfLine(err.Error())
 					_ = conn.Close()
 					return
 				}
 
-				if address == nil {
+				if checkAddress == nil {
 					err = textProto.PrintfLine("535 5.7.8 Authentication failed")
 					if err != nil {
 						_ = textProto.PrintfLine("421 4.7.0 Temporary server error")
@@ -335,7 +339,7 @@ func (fr *Receiver) handleConnection(conn net.Conn) {
 						return
 					}
 				} else {
-					state.AUTH = address
+					state.AUTH = checkAddress
 					err = textProto.PrintfLine("235 2.7.0 Authentication successful")
 					if err != nil {
 						_ = textProto.PrintfLine("421 4.7.0 Temporary server error")
@@ -410,7 +414,14 @@ func (fr *Receiver) handleConnection(conn net.Conn) {
 					continue
 				}
 
-				if *address != *state.AUTH {
+				ok, err := state.AUTH(address)
+				if err != nil {
+					_ = textProto.PrintfLine("421 4.7.0 Temporary server error")
+					_ = conn.Close()
+					return
+				}
+
+				if !ok {
 					err = textProto.PrintfLine("535 5.7.8 Authenticated wrong user")
 					if err != nil {
 						_ = textProto.PrintfLine("421 4.7.0 Temporary server error")
@@ -579,7 +590,6 @@ func (fr *Receiver) handleConnection(conn net.Conn) {
 					Host: strings.Split(conn.RemoteAddr().String(), ":")[0],
 				}
 				go sendEmail(SenderArgs{
-					Hostname:   fr.hostname,
 					EnforceTLS: fr.enforceTLS,
 				}, mail, fr.database, queueID)
 
@@ -608,7 +618,6 @@ func (fr *Receiver) handleConnection(conn net.Conn) {
 
 // SenderArgs is a struct that represents the arguments for the Sender
 type SenderArgs struct {
-	Hostname   string
 	EnforceTLS bool
 }
 
@@ -639,7 +648,7 @@ func Send(args SenderArgs, mail *Mail, conn net.Conn, mxHost string) (err error)
 		return errors.New("unexpected greeting - " + line)
 	}
 
-	err = textConn.PrintfLine("EHLO %s", args.Hostname)
+	err = textConn.PrintfLine("EHLO %s", mxHost)
 	if err != nil {
 		return err
 	}
@@ -673,16 +682,11 @@ func Send(args SenderArgs, mail *Mail, conn net.Conn, mxHost string) (err error)
 			InsecureSkipVerify: false,
 		})
 
-		err = tlsConn.Handshake()
-		if err != nil {
-			return err
-		}
-
 		textConn = textproto.NewConn(tlsConn)
 
 		// Just use HELO, no point using EHLO when we already have all the capabilities
 		// This also gets us out of using readMultilineCodeResponse
-		err = textConn.PrintfLine("HELO %s", args.Hostname)
+		err = textConn.PrintfLine("HELO %s", mxHost)
 		if err != nil {
 			return err
 		}
@@ -705,10 +709,7 @@ func Send(args SenderArgs, mail *Mail, conn net.Conn, mxHost string) (err error)
 	}
 
 	code, line, err = textConn.ReadCodeLine(0)
-	fmt.Println(code, line, err)
 	if err != nil {
-		// For some reason the EHLO stuff ends up here
-		fmt.Println("5")
 		return err
 	}
 
@@ -723,9 +724,7 @@ func Send(args SenderArgs, mail *Mail, conn net.Conn, mxHost string) (err error)
 		}
 
 		code, line, err = textConn.ReadCodeLine(0)
-		fmt.Println(code, line, err)
 		if err != nil {
-			fmt.Println("6")
 			return err
 		}
 
@@ -740,9 +739,7 @@ func Send(args SenderArgs, mail *Mail, conn net.Conn, mxHost string) (err error)
 	}
 
 	code, line, err = textConn.ReadCodeLine(0)
-	fmt.Println(code, line, err)
 	if err != nil {
-		fmt.Println("7")
 		return err
 	}
 
@@ -762,9 +759,7 @@ func Send(args SenderArgs, mail *Mail, conn net.Conn, mxHost string) (err error)
 	}
 
 	code, line, err = textConn.ReadCodeLine(0)
-	fmt.Println(code, line, err)
 	if err != nil {
-		fmt.Println("8")
 		return err
 	}
 
@@ -778,9 +773,7 @@ func Send(args SenderArgs, mail *Mail, conn net.Conn, mxHost string) (err error)
 	}
 
 	code, line, err = textConn.ReadCodeLine(0)
-	fmt.Println(code, line, err)
 	if err != nil {
-		fmt.Println("9")
 		return err
 	}