diff --git a/address.go b/address.go
index 08c5046..1ffce35 100644
--- a/address.go
+++ b/address.go
@@ -5,6 +5,7 @@ import (
 	"strings"
 )
 
+// MailAddress holds an e-mail address
 type MailAddress string
 
 func parseMailAddress(src string) (MailAddress, error) {
diff --git a/protocol.go b/protocol.go
index 0c4ae2d..4c07fad 100644
--- a/protocol.go
+++ b/protocol.go
@@ -94,6 +94,11 @@ func (session *session) handleMAIL(cmd command) {
 		return
 	}
 
+	if !session.tls && session.server.ForceTLS {
+		session.reply(502, "Please turn on TLS by issuing a STARTTLS command.")
+		return
+	}
+
 	addr, err := parseMailAddress(cmd.params[1])
 
 	if err != nil {
@@ -157,18 +162,18 @@ func (session *session) handleSTARTTLS(cmd command) {
 		return
 	}
 
-	tls_conn := tls.Server(session.conn, session.server.TLSConfig)
+	tlsConn := tls.Server(session.conn, session.server.TLSConfig)
 	session.reply(250, "Go ahead")
 
-	if err := tls_conn.Handshake(); err != nil {
+	if err := tlsConn.Handshake(); err != nil {
 		log.Printf("TLS Handshake error:", err)
 		session.reply(550, "Handshake error")
 		return
 	}
 
-	session.conn = tls_conn
-	session.reader = bufio.NewReader(tls_conn)
-	session.writer = bufio.NewWriter(tls_conn)
+	session.conn = tlsConn
+	session.reader = bufio.NewReader(tlsConn)
+	session.writer = bufio.NewWriter(tlsConn)
 	session.scanner = bufio.NewScanner(session.reader)
 	session.tls = true
 
@@ -206,6 +211,14 @@ func (session *session) handleDATA(cmd command) {
 		return
 	}
 
+	if data.Len() > session.server.MaxMessageSize {
+		session.reply(550, fmt.Sprintf(
+			"Message exceeded max message size of %d bytes",
+			session.server.MaxMessageSize,
+		))
+		return
+	}
+
 	session.envelope.Data = data.Bytes()
 
 	err := session.deliver()
@@ -283,7 +296,7 @@ func (session *session) handleAUTH(cmd command) {
 			return
 		}
 
-		byte_username, err := base64.StdEncoding.DecodeString(session.scanner.Text())
+		byteUsername, err := base64.StdEncoding.DecodeString(session.scanner.Text())
 
 		if err != nil {
 			session.reply(502, "Couldn't decode your credentials")
@@ -296,15 +309,15 @@ func (session *session) handleAUTH(cmd command) {
 			return
 		}
 
-		byte_password, err := base64.StdEncoding.DecodeString(session.scanner.Text())
+		bytePassword, err := base64.StdEncoding.DecodeString(session.scanner.Text())
 
 		if err != nil {
 			session.reply(502, "Couldn't decode your credentials")
 			return
 		}
 
-		username = string(byte_username)
-		password = string(byte_password)
+		username = string(byteUsername)
+		password = string(bytePassword)
 
 	default:
 
diff --git a/smtpd.go b/smtpd.go
index 3de37cc..c2b0194 100644
--- a/smtpd.go
+++ b/smtpd.go
@@ -11,6 +11,7 @@ import (
 	"time"
 )
 
+// Server defines the parameters for running the SMTP server
 type Server struct {
 	Addr           string // Address to listen on when using ListenAndServe (default: "127.0.0.1:10025")
 	WelcomeMessage string // Initial server banner (default: "<hostname> ESMTP ready.")
@@ -40,13 +41,15 @@ type Server struct {
 	MaxMessageSize int // Max message size in bytes (default: 10240000)
 }
 
+// Peer represents the client connecting to the server
 type Peer struct {
 	HeloName string   // Server name used in HELO/EHLO command
-	Username string   // Username from authentication
-	Password string   // Password from authentication
+	Username string   // Username from authentication, if authenticated
+	Password string   // Password from authentication, if authenticated
 	Addr     net.Addr // Network address
 }
 
+// Envelope holds a message
 type Envelope struct {
 	Sender     MailAddress
 	Recipients []MailAddress
@@ -86,6 +89,7 @@ func (srv *Server) newSession(c net.Conn) (s *session, err error) {
 
 }
 
+// ListenAndServe starts the SMTP server and listens on the address provided in Server.Addr
 func (srv *Server) ListenAndServe() error {
 
 	srv.configureDefaults()
@@ -98,6 +102,7 @@ func (srv *Server) ListenAndServe() error {
 	return srv.Serve(l)
 }
 
+// Serve starts the SMTP server and listens on the Listener provided
 func (srv *Server) Serve(l net.Listener) error {
 
 	srv.configureDefaults()
@@ -243,7 +248,7 @@ func (session *session) error(err error) {
 func (session *session) extensions() []string {
 
 	extensions := []string{
-		"SIZE 10240000",
+		fmt.Sprintf("SIZE %d", session.server.MaxMessageSize),
 	}
 
 	if session.server.TLSConfig != nil && !session.tls {
@@ -261,9 +266,8 @@ func (session *session) extensions() []string {
 func (session *session) deliver() error {
 	if session.server.Handler != nil {
 		return session.server.Handler(session.peer, *session.envelope)
-	} else {
-		return nil
 	}
+	return nil
 }
 
 func (session *session) close() {