diff --git a/protocol.go b/protocol.go
index ab5c217..bf783a3 100644
--- a/protocol.go
+++ b/protocol.go
@@ -38,6 +38,10 @@ func (session *session) handle(line string) {
 
 	cmd := parseLine(line)
 
+	// Commands are dispatched to the appropriate handler functions.
+	// If a network error occurs during handling, the handler should
+	// just return and let the error be handled on the next read.
+
 	switch cmd.action {
 
 	case "HELO":
@@ -95,7 +99,7 @@ func (session *session) handleHELO(cmd command) {
 
 	if session.peer.HeloName != "" {
 		// Reset envelope in case of duplicate HELO
-		session.envelope = nil
+		session.reset()
 	}
 
 	if session.server.HeloChecker != nil {
@@ -122,7 +126,7 @@ func (session *session) handleEHLO(cmd command) {
 
 	if session.peer.HeloName != "" {
 		// Reset envelope in case of duplicate EHLO
-		session.envelope = nil
+		session.reset()
 	}
 
 	if session.server.HeloChecker != nil {
@@ -197,7 +201,7 @@ func (session *session) handleRCPT(cmd command) {
 	}
 
 	if len(session.envelope.Recipients) >= session.server.MaxRecipients {
-		session.reply(550, "Too many recipients")
+		session.reply(452, "Too many recipients")
 		return
 	}
 
@@ -243,7 +247,7 @@ func (session *session) handleSTARTTLS(cmd command) {
 	}
 
 	// Reset envelope as a new EHLO/HELO is required after STARTTLS
-	session.envelope = nil
+	session.reset()
 
 	// Reset deadlines on the underlying connection before I replace it
 	// with a TLS connection
@@ -291,7 +295,7 @@ func (session *session) handleDATA(cmd command) {
 			session.reply(250, "Thank you.")
 		}
 
-		session.envelope = nil
+		session.reset()
 
 	}
 
@@ -313,14 +317,14 @@ func (session *session) handleDATA(cmd command) {
 		session.server.MaxMessageSize,
 	))
 
-	session.envelope = nil
+	session.reset()
 
 	return
 
 }
 
 func (session *session) handleRSET(cmd command) {
-	session.envelope = nil
+	session.reset()
 	session.reply(250, "Go ahead")
 	return
 }
diff --git a/smtpd.go b/smtpd.go
index ac6585d..490a546 100644
--- a/smtpd.go
+++ b/smtpd.go
@@ -214,8 +214,31 @@ func (session *session) serve() {
 
 	session.welcome()
 
-	for session.scanner.Scan() {
-		session.handle(session.scanner.Text())
+	for {
+
+		for session.scanner.Scan() {
+			session.handle(session.scanner.Text())
+		}
+
+		err := session.scanner.Err()
+
+		if err == bufio.ErrTooLong {
+
+			session.reply(500, "Line too long")
+
+			// Advance reader to the next newline
+
+			session.reader.ReadString('\n')
+			session.scanner = bufio.NewScanner(session.reader)
+
+			// Reset and have the client start over.
+
+			session.reset()
+
+			continue
+		}
+
+		break
 	}
 
 }
@@ -225,6 +248,10 @@ func (session *session) reject() {
 	session.close()
 }
 
+func (session *session) reset() {
+	session.envelope = nil
+}
+
 func (session *session) welcome() {
 
 	if session.server.ConnectionChecker != nil {
diff --git a/smtpd_test.go b/smtpd_test.go
index f13b200..a8b47a6 100644
--- a/smtpd_test.go
+++ b/smtpd_test.go
@@ -1028,3 +1028,33 @@ func TestTLSTimeout(t *testing.T) {
 	}
 
 }
+
+func TestLongLine(t *testing.T) {
+
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("Listen failed: %v", err)
+	}
+
+	defer ln.Close()
+
+	server := &smtpd.Server{}
+
+	go func() {
+		server.Serve(ln)
+	}()
+
+	c, err := smtp.Dial(ln.Addr().String())
+	if err != nil {
+		t.Fatalf("Dial failed: %v", err)
+	}
+
+	if err := c.Mail(fmt.Sprintf("%s@example.org", strings.Repeat("x", 65*1024))); err == nil {
+		t.Fatalf("MAIL failed: %v", err)
+	}
+
+	if err := c.Quit(); err != nil {
+		t.Fatalf("Quit failed: %v", err)
+	}
+
+}