diff --git a/onceCloseListerner.go b/onceCloseListerner.go
new file mode 100644
index 0000000..4f4926c
--- /dev/null
+++ b/onceCloseListerner.go
@@ -0,0 +1,28 @@
+package smtpd
+
+import (
+	"net"
+	"sync"
+	"sync/atomic"
+)
+
+// onceCloseListener wraps a net.Listener, protecting it from
+// multiple Close calls.
+type onceCloseListener struct {
+	net.Listener
+	once     sync.Once
+	closeErr error
+}
+
+func (oc *onceCloseListener) Close() error {
+	oc.once.Do(oc.close)
+	return oc.closeErr
+}
+
+func (oc *onceCloseListener) close() { oc.closeErr = oc.Listener.Close() }
+
+type atomicBool int32
+
+func (b *atomicBool) isSet() bool { return atomic.LoadInt32((*int32)(b)) != 0 }
+func (b *atomicBool) setTrue()    { atomic.StoreInt32((*int32)(b), 1) }
+func (b *atomicBool) setFalse()   { atomic.StoreInt32((*int32)(b), 0) }
diff --git a/session.go b/session.go
new file mode 100644
index 0000000..44d6550
--- /dev/null
+++ b/session.go
@@ -0,0 +1,163 @@
+package smtpd
+
+import (
+  "net"
+  "bufio"
+  "strings"
+  "fmt"
+  "time"
+)
+
+type session struct {
+	server *Server
+
+	peer     Peer
+	envelope *Envelope
+
+	conn net.Conn
+
+	reader  *bufio.Reader
+	writer  *bufio.Writer
+	scanner *bufio.Scanner
+
+	tls bool
+}
+
+
+func (session *session) serve() {
+
+	defer session.close()
+
+	if !session.server.EnableProxyProtocol {
+		session.welcome()
+	}
+
+	for {
+
+		for session.scanner.Scan() {
+			line := session.scanner.Text()
+			session.logf("received: %s", strings.TrimSpace(line))
+			session.handle(line)
+		}
+
+		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
+	}
+
+}
+
+func (session *session) reject() {
+	session.reply(421, "Too busy. Try again later.")
+	session.close()
+}
+
+func (session *session) reset() {
+	session.envelope = nil
+}
+
+func (session *session) welcome() {
+
+	if session.server.ConnectionChecker != nil {
+		err := session.server.ConnectionChecker(session.peer)
+		if err != nil {
+			session.error(err)
+			session.close()
+			return
+		}
+	}
+
+	session.reply(220, session.server.WelcomeMessage)
+
+}
+
+func (session *session) reply(code int, message string) {
+	session.logf("sending: %d %s", code, message)
+	fmt.Fprintf(session.writer, "%d %s\r\n", code, message)
+	session.flush()
+}
+
+func (session *session) flush() {
+	session.conn.SetWriteDeadline(time.Now().Add(session.server.WriteTimeout))
+	session.writer.Flush()
+	session.conn.SetReadDeadline(time.Now().Add(session.server.ReadTimeout))
+}
+
+func (session *session) error(err error) {
+	if smtpdError, ok := err.(Error); ok {
+		session.reply(smtpdError.Code, smtpdError.Message)
+	} else {
+		session.reply(502, fmt.Sprintf("%s", err))
+	}
+}
+
+func (session *session) logf(format string, v ...interface{}) {
+	if session.server.ProtocolLogger == nil {
+		return
+	}
+	session.server.ProtocolLogger.Info(fmt.Sprintf(
+		"%s [peer:%s]",
+		fmt.Sprintf(format, v...),
+		session.peer.Addr,
+	))
+
+}
+
+func (session *session) logError(err error, desc string) {
+	session.server.ProtocolLogger.Error(desc, "error", err)
+}
+
+func (session *session) extensions() []string {
+
+	extensions := []string{
+		fmt.Sprintf("SIZE %d", session.server.MaxMessageSize),
+		"8BITMIME",
+		"PIPELINING",
+	}
+
+	if session.server.EnableXCLIENT {
+		extensions = append(extensions, "XCLIENT")
+	}
+
+	if session.server.TLSConfig != nil && !session.tls {
+		extensions = append(extensions, "STARTTLS")
+	}
+
+	if session.server.Authenticator != nil && session.tls {
+		extensions = append(extensions, "AUTH PLAIN LOGIN")
+	}
+
+	return extensions
+
+}
+
+func (session *session) deliver() error {
+	if session.server.Handler != nil {
+		return session.server.Handler(session.peer, *session.envelope)
+	}
+	return nil
+}
+
+func (session *session) close() {
+	session.writer.Flush()
+	time.Sleep(200 * time.Millisecond)
+	session.conn.Close()
+}
+
+
diff --git a/smtpd.go b/smtpd.go
index d31651f..a24729f 100644
--- a/smtpd.go
+++ b/smtpd.go
@@ -9,9 +9,7 @@ import (
 	"log/slog"
   "log"
 	"net"
-	"strings"
 	"sync"
-	"sync/atomic"
 	"time"
 )
 
@@ -98,21 +96,6 @@ func (e Error) Error() string { return fmt.Sprintf("%d %s", e.Code, e.Message) }
 // methods after a call to Shutdown.
 var ErrServerClosed = errors.New("smtp: Server closed")
 
-type session struct {
-	server *Server
-
-	peer     Peer
-	envelope *Envelope
-
-	conn net.Conn
-
-	reader  *bufio.Reader
-	writer  *bufio.Writer
-	scanner *bufio.Scanner
-
-	tls bool
-}
-
 func (srv *Server) newSession(c net.Conn) (s *session) {
 
 	s = &session{
@@ -298,143 +281,6 @@ func (srv *Server) configureDefaults() {
 
 }
 
-func (session *session) serve() {
-
-	defer session.close()
-
-	if !session.server.EnableProxyProtocol {
-		session.welcome()
-	}
-
-	for {
-
-		for session.scanner.Scan() {
-			line := session.scanner.Text()
-			session.logf("received: %s", strings.TrimSpace(line))
-			session.handle(line)
-		}
-
-		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
-	}
-
-}
-
-func (session *session) reject() {
-	session.reply(421, "Too busy. Try again later.")
-	session.close()
-}
-
-func (session *session) reset() {
-	session.envelope = nil
-}
-
-func (session *session) welcome() {
-
-	if session.server.ConnectionChecker != nil {
-		err := session.server.ConnectionChecker(session.peer)
-		if err != nil {
-			session.error(err)
-			session.close()
-			return
-		}
-	}
-
-	session.reply(220, session.server.WelcomeMessage)
-
-}
-
-func (session *session) reply(code int, message string) {
-	session.logf("sending: %d %s", code, message)
-	fmt.Fprintf(session.writer, "%d %s\r\n", code, message)
-	session.flush()
-}
-
-func (session *session) flush() {
-	session.conn.SetWriteDeadline(time.Now().Add(session.server.WriteTimeout))
-	session.writer.Flush()
-	session.conn.SetReadDeadline(time.Now().Add(session.server.ReadTimeout))
-}
-
-func (session *session) error(err error) {
-	if smtpdError, ok := err.(Error); ok {
-		session.reply(smtpdError.Code, smtpdError.Message)
-	} else {
-		session.reply(502, fmt.Sprintf("%s", err))
-	}
-}
-
-func (session *session) logf(format string, v ...interface{}) {
-	if session.server.ProtocolLogger == nil {
-		return
-	}
-	session.server.ProtocolLogger.Info(fmt.Sprintf(
-		"%s [peer:%s]",
-		fmt.Sprintf(format, v...),
-		session.peer.Addr,
-	))
-
-}
-
-func (session *session) logError(err error, desc string) {
-	session.server.ProtocolLogger.Error(desc, "error", err)
-}
-
-func (session *session) extensions() []string {
-
-	extensions := []string{
-		fmt.Sprintf("SIZE %d", session.server.MaxMessageSize),
-		"8BITMIME",
-		"PIPELINING",
-	}
-
-	if session.server.EnableXCLIENT {
-		extensions = append(extensions, "XCLIENT")
-	}
-
-	if session.server.TLSConfig != nil && !session.tls {
-		extensions = append(extensions, "STARTTLS")
-	}
-
-	if session.server.Authenticator != nil && session.tls {
-		extensions = append(extensions, "AUTH PLAIN LOGIN")
-	}
-
-	return extensions
-
-}
-
-func (session *session) deliver() error {
-	if session.server.Handler != nil {
-		return session.server.Handler(session.peer, *session.envelope)
-	}
-	return nil
-}
-
-func (session *session) close() {
-	session.writer.Flush()
-	time.Sleep(200 * time.Millisecond)
-	session.conn.Close()
-}
-
-
 // From net/http/server.go
 
 func (s *Server) shuttingDown() bool {
@@ -466,23 +312,3 @@ func (s *Server) closeDoneChanLocked() {
 	}
 }
 
-// onceCloseListener wraps a net.Listener, protecting it from
-// multiple Close calls.
-type onceCloseListener struct {
-	net.Listener
-	once     sync.Once
-	closeErr error
-}
-
-func (oc *onceCloseListener) Close() error {
-	oc.once.Do(oc.close)
-	return oc.closeErr
-}
-
-func (oc *onceCloseListener) close() { oc.closeErr = oc.Listener.Close() }
-
-type atomicBool int32
-
-func (b *atomicBool) isSet() bool { return atomic.LoadInt32((*int32)(b)) != 0 }
-func (b *atomicBool) setTrue()    { atomic.StoreInt32((*int32)(b), 1) }
-func (b *atomicBool) setFalse()   { atomic.StoreInt32((*int32)(b), 0) }