diff --git a/server.go b/server.go
index 5b92ccf..5249870 100644
--- a/server.go
+++ b/server.go
@@ -8,7 +8,6 @@ import (
 	"log"
 	"net"
 	"os"
-	"strings"
 	"sync"
 	"time"
 
@@ -30,11 +29,13 @@ type Logger interface {
 
 // A SMTP server.
 type Server struct {
+	// The type of network, "tcp" or "unix".
+	Network string
 	// TCP or Unix address to listen on.
 	Addr string
 	// The server TLS configuration.
 	TLSConfig *tls.Config
-	// Enable LMTP mode.
+	// Enable LMTP mode, as defined in RFC 2033.
 	LMTP bool
 
 	Domain            string
@@ -213,13 +214,17 @@ func (s *Server) handleConn(c *Conn) error {
 // ListenAndServe listens on the network address s.Addr and then calls Serve
 // to handle requests on incoming connections.
 //
-// If s.Addr is blank and LMTP is disabled, ":smtp" is used. If it is enabled,
-// ":24" (any private mail system) is used.
-// If s.Addr contains "/", UNIX domain socket is used. Otherwise TCP socket
-// is used.
+// If s.Network is "tcp" (default) and s.Addr is blank, ":24" (any private
+// mail system) for LMTP or ":smtp" for (E)SMTP is used.
+// If s.Network is "unix", s.Addr must be given explicitly.
 func (s *Server) ListenAndServe() error {
+	network := s.Network
+	if network == "" {
+		network = "tcp"
+	}
+
 	addr := s.Addr
-	if addr == "" {
+	if addr == "" && network == "tcp" {
 		if s.LMTP {
 			addr = ":24"
 		} else {
@@ -227,11 +232,6 @@ func (s *Server) ListenAndServe() error {
 		}
 	}
 
-	network := "tcp"
-	if strings.Contains(addr, "/") {
-		network = "unix"
-	}
-
 	l, err := net.Listen(network, addr)
 	if err != nil {
 		return err
@@ -243,18 +243,18 @@ func (s *Server) ListenAndServe() error {
 // ListenAndServeTLS listens on the TCP network address s.Addr and then calls
 // Serve to handle requests on incoming TLS connections.
 //
-// If s.Addr is blank, ":465" (Message Submission over TLS) is used.
-// If s.Addr contains "/", UNIX domain socket is used. Otherwise TCP socket
-// is used.
+// If s.Network is "tcp" (default) and s.Addr is blank, ":465" (Message
+// Submission over TLS) is used.
+// If s.Network is "unix", s.Addr must be given explicitly.
 func (s *Server) ListenAndServeTLS() error {
-	addr := s.Addr
-	if addr == "" {
-		addr = ":465"
+	network := s.Network
+	if network == "" {
+		network = "tcp"
 	}
 
-	network := "tcp"
-	if strings.Contains(addr, "/") {
-		network = "unix"
+	addr := s.Addr
+	if addr == "" && network == "tcp" {
+		addr = ":465"
 	}
 
 	l, err := tls.Listen(network, addr, s.TLSConfig)