diff --git a/cmd/warp/main.go b/cmd/warp/main.go
index 6d0354b..fff2c3c 100644
--- a/cmd/warp/main.go
+++ b/cmd/warp/main.go
@@ -17,6 +17,7 @@ var (
 	port    = flag.Int("port", 0, "listen port")
 	oip     = flag.String("outbound-ip", "0.0.0.0", "outbound ip")
 	storage = flag.String("storage", "", "sspecify extended storage from: mysql, sqlite, file")
+	maxSize = flag.Int("message-size-limit", 10240000, "The maximal size in bytes of a message")
 	verbose = flag.Bool("verbose", false, "verbose logging")
 	verFlag = flag.Bool("version", false, "show build version")
 )
@@ -32,10 +33,11 @@ func main() {
 	}
 
 	w := &warp.Server{
-		Addr:         *ip,
-		Port:         *port,
-		OutboundAddr: *oip,
-		Verbose:      *verbose,
+		Addr:             *ip,
+		Port:             *port,
+		OutboundAddr:     *oip,
+		Verbose:          *verbose,
+		MessageSizeLimit: *maxSize,
 	}
 
 	switch *storage {
diff --git a/pipe.go b/pipe.go
index 9eb76b1..54ae663 100644
--- a/pipe.go
+++ b/pipe.go
@@ -14,9 +14,10 @@ import (
 )
 
 type Pipe struct {
-	id    string
-	sConn net.Conn
-	rConn net.Conn
+	id         string
+	sConn      net.Conn
+	rConn      net.Conn
+	bufferSize int
 
 	rAddr       *net.TCPAddr
 	sMailAddr   []byte
@@ -29,6 +30,8 @@ type Pipe struct {
 	locked   bool
 	blocker  chan interface{}
 
+	isWaitedStarttlsRes bool
+
 	timeAtConnected    time.Time
 	timeAtDataStarting time.Time
 
@@ -46,7 +49,6 @@ const (
 	mailFromPrefix string = "MAIL FROM:<"
 	rcptToPrefix   string = "RCPT TO:<"
 	mailRegex      string = `[A-z0-9.!#$%&'*+\-/=?^_\{|}~]{1,64}@[A-z0-9.\-]{1,255}`
-	bufferSize     int    = 32 * 1024
 	crlf           string = "\r\n"
 	mailHeaderEnd  string = crlf + crlf
 
@@ -91,6 +93,7 @@ func (p *Pipe) mediateOnUpstream(b []byte, i int) ([]byte, int, bool) {
 	if !p.tls && p.readytls {
 		p.locked = true
 		er := p.starttls()
+		p.isWaitedStarttlsRes = true
 		if er != nil {
 			go p.afterCommHook([]byte(fmt.Sprintf("starttls error: %s", er.Error())), pxyToDst)
 		}
@@ -123,15 +126,15 @@ func (p *Pipe) mediateOnDownstream(b []byte, i int) ([]byte, int, bool) {
 		}
 	}
 
-	// time before email input
-	p.setTimeAtDataStarting(b)
-
-	// remove buffering ready response
-	if p.tls && !p.readytls && p.locked {
-		// continue
+	// remove buffering "220 2.0.0 Ready to start TLS" response
+	if p.isWaitedStarttlsRes {
+		p.isWaitedStarttlsRes = false
 		return b, i, true
 	}
 
+	// time before email input
+	p.setTimeAtDataStarting(b)
+
 	if p.isResponseOfEHLOWithoutStartTLS(b) {
 		go p.afterCommHook(data, pxyToSrc)
 	} else {
@@ -213,7 +216,7 @@ func (p *Pipe) dst(d Flow) net.Conn {
 }
 
 func (p *Pipe) copy(dr Flow, fn Mediator) (written int64, err error) {
-	size := bufferSize
+	size := p.bufferSize
 	src, ok := p.src(dr).(io.Reader)
 	if !ok {
 		err = fmt.Errorf("io.Reader cast error")
@@ -226,7 +229,7 @@ func (p *Pipe) copy(dr Flow, fn Mediator) (written int64, err error) {
 		}
 		go p.afterCommHook([]byte(fmt.Sprintf("io.Reader size: %d", size)), onPxy)
 	}
-	buf := make([]byte, bufferSize)
+	buf := make([]byte, p.bufferSize)
 
 	for {
 		var isContinue bool
@@ -284,7 +287,7 @@ func (p *Pipe) starttls() error {
 }
 
 func (p *Pipe) readReceiverConn() error {
-	buf := make([]byte, bufferSize)
+	buf := make([]byte, 64*1024)
 	i, err := p.rConn.Read(buf)
 	if err != nil {
 		return err
diff --git a/server.go b/server.go
index 7b3d4ee..06980dc 100644
--- a/server.go
+++ b/server.go
@@ -12,12 +12,13 @@ import (
 const SO_ORIGINAL_DST = 80
 
 type Server struct {
-	Addr         string
-	Port         int
-	Hooks        []Hook
-	OutboundAddr string
-	Verbose      bool
-	log          *log.Logger
+	Addr             string
+	Port             int
+	Hooks            []Hook
+	OutboundAddr     string
+	Verbose          bool
+	log              *log.Logger
+	MessageSizeLimit int
 }
 
 // These are global variables for integration test.
@@ -30,6 +31,10 @@ func (s *Server) Start() error {
 	if s.log == nil {
 		s.log = log.New(os.Stderr, "", log.Ldate|log.Ltime|log.Lmicroseconds)
 	}
+	if s.MessageSizeLimit == 0 {
+		// default is around 10MB (https://www.postfix.org/postconf.5.html)
+		s.MessageSizeLimit = 10240000
+	}
 
 	pl := &Plugins{}
 	if err := pl.load(); err != nil {
@@ -109,10 +114,11 @@ func (s *Server) HandleConnection(conn net.Conn) {
 	}
 
 	p := &Pipe{
-		id:    uuid,
-		sConn: conn,
-		rConn: dstConn,
-		rAddr: raddr,
+		id:         uuid,
+		sConn:      conn,
+		rConn:      dstConn,
+		rAddr:      raddr,
+		bufferSize: s.MessageSizeLimit,
 	}
 	p.afterCommHook = func(b Data, to Direction) {
 		now := time.Now()