Add new field Banner in Server struct for custom smtp greeting text

conn.go

@@ -140,7 +140,7 @@ func (c *Conn) handle(cmd string, arg string) {
 	case "DATA":
 		c.handleData(arg)
 	case "QUIT":
-		c.WriteResponse(221, EnhancedCode{2, 0, 0}, "Goodnight and good luck")
+		c.WriteResponse(221, EnhancedCode{2, 0, 0}, "Bye")
 		c.Close()
 	case "AUTH":
 		if c.server.AuthDisabled {
@@ -934,7 +934,7 @@ func (c *Conn) Reject() {
 }
 
 func (c *Conn) greet() {
-	c.WriteResponse(220, NoEnhancedCode, fmt.Sprintf("%v ESMTP Service Ready", c.server.Domain))
+	c.WriteResponse(220, NoEnhancedCode, c.server.Banner)
 }
 
 func (c *Conn) WriteResponse(code int, enhCode EnhancedCode, text ...string) {

example_test.go

@@ -140,6 +140,7 @@ func ExampleNewServer() {
 
 	s.Addr = ":1025"
 	s.Domain = "localhost"
+	s.Banner = s.Domain + " ESMTP Server Ready"
 	s.WriteTimeout = 10 * time.Second
 	s.ReadTimeout = 10 * time.Second
 	s.MaxMessageBytes = 1024 * 1024

server.go

@@ -45,6 +45,9 @@ type Server struct {
 	ReadTimeout       time.Duration
 	WriteTimeout      time.Duration
 
+	// The text that follows the 220 status code in the SMTP greeting banner.
+	Banner string
+
 	// Advertise SMTPUTF8 (RFC 6531) capability.
 	// Should be used only if backend supports it.
 	EnableSMTPUTF8 bool
@@ -75,7 +78,7 @@ type Server struct {
 
 // New creates a new SMTP server.
 func NewServer(be Backend) *Server {
-	return &Server{
+	s := &Server{
 		// Doubled maximum line length per RFC 5321 (Section 4.5.3.1.6)
 		MaxLineLength: 2000,
 
@@ -103,6 +106,14 @@ func NewServer(be Backend) *Server {
 		},
 		conns: make(map[*Conn]struct{}),
 	}
+
+	if s.Banner == "" {
+		s.Banner = s.Domain + " ESMTP Service Ready"
+	} else {
+		s.Banner = s.Domain + " " + s.Banner
+	}
+
+	return s
 }
 
 // Serve accepts incoming connections on the Listener l.

server_test.go

@@ -171,7 +171,7 @@ func testServer(t *testing.T, fn ...serverConfigureFunc) (be *backend, s *smtp.S
 
 	be = new(backend)
 	s = smtp.NewServer(be)
-	s.Domain = "localhost"
+	s.Banner = "localhost ESMTP Service Ready"
 	s.AllowInsecureAuth = true
 	for _, f := range fn {
 		f(s)
@@ -728,7 +728,6 @@ func testStrictServer(t *testing.T) (s *smtp.Server, c net.Conn, scanner *bufio.
 	}
 
 	s = smtp.NewServer(new(backend))
-	s.Domain = "localhost"
 	s.AllowInsecureAuth = true
 	s.AuthDisabled = true
 	s.Strict = true