diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 52c5d813eb..a195f2664d 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -146,8 +146,8 @@ module Net
   # The SMTP server will judge whether it should send or reject
   # the SMTP session by inspecting the HELO domain.
   #
-  #     Net::SMTP.start('your.smtp.server', 25,
-  #                     'mail.from.domain') { |smtp| ... }
+  #     Net::SMTP.start('your.smtp.server', 25
+  #                     helo: 'mail.from.domain') { |smtp| ... }
   #
   # === SMTP Authentication
   #
@@ -157,15 +157,15 @@ module Net
   # SMTP.start/SMTP#start.
   #
   #     # PLAIN
-  #     Net::SMTP.start('your.smtp.server', 25, 'mail.from.domain',
-  #                     'Your Account', 'Your Password', :plain)
+  #     Net::SMTP.start('your.smtp.server', 25
+  #                     user: 'Your Account', secret: 'Your Password', authtype: :plain)
   #     # LOGIN
-  #     Net::SMTP.start('your.smtp.server', 25, 'mail.from.domain',
-  #                     'Your Account', 'Your Password', :login)
+  #     Net::SMTP.start('your.smtp.server', 25
+  #                     user: 'Your Account', secret: 'Your Password', authtype: :login)
   #
   #     # CRAM MD5
-  #     Net::SMTP.start('your.smtp.server', 25, 'mail.from.domain',
-  #                     'Your Account', 'Your Password', :cram_md5)
+  #     Net::SMTP.start('your.smtp.server', 25
+  #                     user: 'Your Account', secret: 'Your Password', authtype: :cram_md5)
   #
   class SMTP < Protocol
     VERSION = "0.1.0"
@@ -401,12 +401,16 @@ module Net
     # SMTP session control
     #
 
+    #
+    # :call-seq:
+    #  start(address, port = nil, helo: 'localhost', user: nil, secret: nil, authtype: nil) { |smtp| ... }
+    #  start(address, port = nil, helo = 'localhost', user = nil, secret = nil, authtype = nil) { |smtp| ... }
     #
     # Creates a new Net::SMTP object and connects to the server.
     #
     # This method is equivalent to:
     #
-    #   Net::SMTP.new(address, port).start(helo_domain, account, password, authtype)
+    #   Net::SMTP.new(address, port).start(helo: helo_domain, user: account, secret: password, authtype: authtype)
     #
     # === Example
     #
@@ -450,10 +454,15 @@ module Net
     # * Net::ReadTimeout
     # * IOError
     #
-    def SMTP.start(address, port = nil, helo = 'localhost',
-                   user = nil, secret = nil, authtype = nil,
-                   &block)   # :yield: smtp
-      new(address, port).start(helo, user, secret, authtype, &block)
+    def SMTP.start(address, port = nil, *args, helo: nil,
+                   user: nil, secret: nil, password: nil, authtype: nil,
+                   &block)
+      raise ArgumentError, "wrong number of arguments (given #{args.size + 2}, expected 1..6)" if args.size > 4
+      helo ||= args[0] || 'localhost'
+      user ||= args[1]
+      secret ||= password || args[2]
+      authtype ||= args[3]
+      new(address, port).start(helo: helo, user: user, secret: secret, authtype: authtype, &block)
     end
 
     # +true+ if the SMTP session has been started.
@@ -461,6 +470,10 @@ module Net
       @started
     end
 
+    #
+    # :call-seq:
+    #  start(helo: 'localhost', user: nil, secret: nil, authtype: nil) { |smtp| ... }
+    #  start(helo = 'localhost', user = nil, secret = nil, authtype = nil) { |smtp| ... }
     #
     # Opens a TCP connection and starts the SMTP session.
     #
@@ -488,7 +501,7 @@ module Net
     #
     #     require 'net/smtp'
     #     smtp = Net::SMTP.new('smtp.mail.server', 25)
-    #     smtp.start(helo_domain, account, password, authtype) do |smtp|
+    #     smtp.start(helo: helo_domain, user: account, secret: password, authtype: authtype) do |smtp|
     #       smtp.send_message msgstr, 'from@example.com', ['dest@example.com']
     #     end
     #
@@ -512,8 +525,13 @@ module Net
     # * Net::ReadTimeout
     # * IOError
     #
-    def start(helo = 'localhost',
-              user = nil, secret = nil, authtype = nil)   # :yield: smtp
+    def start(*args, helo: nil,
+              user: nil, secret: nil, password: nil, authtype: nil)
+      raise ArgumentError, "wrong number of arguments (given #{args.size}, expected 0..4)" if args.size > 4
+      helo ||= args[0] || 'localhost'
+      user ||= args[1]
+      secret ||= password || args[2]
+      authtype ||= args[3]
       if block_given?
         begin
           do_start helo, user, secret, authtype
diff --git a/test/net/smtp/test_smtp.rb b/test/net/smtp/test_smtp.rb
index 90c92e06f8..507caee025 100644
--- a/test/net/smtp/test_smtp.rb
+++ b/test/net/smtp/test_smtp.rb
@@ -184,17 +184,99 @@ module Net
       end
     end
 
+    def test_start
+      port = fake_server_start
+      smtp = Net::SMTP.start('localhost', port)
+      smtp.quit
+    end
+
+    def test_start_with_position_argument
+      port = fake_server_start(helo: 'myname', user: 'account', password: 'password')
+      smtp = Net::SMTP.start('localhost', port, 'myname', 'account', 'password', :plain)
+      smtp.quit
+    end
+
+    def test_start_with_keyword_argument
+      port = fake_server_start(helo: 'myname', user: 'account', password: 'password')
+      smtp = Net::SMTP.start('localhost', port, helo: 'myname', user: 'account', secret: 'password', authtype: :plain)
+      smtp.quit
+    end
+
+    def test_start_password_is_secret
+      port = fake_server_start(helo: 'myname', user: 'account', password: 'password')
+      smtp = Net::SMTP.start('localhost', port, helo: 'myname', user: 'account', password: 'password', authtype: :plain)
+      smtp.quit
+    end
+
+    def test_start_invalid_number_of_arguments
+      err = assert_raise ArgumentError do
+        Net::SMTP.start('localhost', 25, 'myname', 'account', 'password', :plain, :invalid_arg)
+      end
+      assert_equal('wrong number of arguments (given 7, expected 1..6)', err.message)
+    end
+
+    def test_start_instance
+      port = fake_server_start
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start
+      smtp.quit
+    end
+
+    def test_start_instance_with_position_argument
+      port = fake_server_start(helo: 'myname', user: 'account', password: 'password')
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start('myname', 'account', 'password', :plain)
+      smtp.quit
+    end
+
+    def test_start_instance_with_keyword_argument
+      port = fake_server_start(helo: 'myname', user: 'account', password: 'password')
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start(helo: 'myname', user: 'account', secret: 'password', authtype: :plain)
+      smtp.quit
+    end
+
+    def test_start_instance_password_is_secret
+      port = fake_server_start(helo: 'myname', user: 'account', password: 'password')
+      smtp = Net::SMTP.new('localhost', port)
+      smtp.start(helo: 'myname', user: 'account', password: 'password', authtype: :plain)
+      smtp.quit
+    end
+
+    def test_start_instance_invalid_number_of_arguments
+      smtp = Net::SMTP.new('localhost')
+      err = assert_raise ArgumentError do
+        smtp.start('myname', 'account', 'password', :plain, :invalid_arg)
+      end
+      assert_equal('wrong number of arguments (given 5, expected 0..4)', err.message)
+    end
+
     private
 
     def accept(servers)
-      loop do
-        readable, = IO.select(servers.map(&:to_io))
-        readable.each do |r|
-          sock, = r.accept_nonblock(exception: false)
-          next if sock == :wait_readable
-          return sock
+      Socket.accept_loop(servers) { |s, _| break s }
+    end
+
+    def fake_server_start(helo: 'localhost', user: nil, password: nil)
+      servers = Socket.tcp_server_sockets('localhost', 0)
+      Thread.start do
+        Thread.current.abort_on_exception = true
+        sock = accept(servers)
+        sock.puts "220 ready\r\n"
+        assert_equal("EHLO #{helo}\r\n", sock.gets)
+        sock.puts "220-servername\r\n220 AUTH PLAIN\r\n"
+        if user
+          credential = ["\0#{user}\0#{password}"].pack('m0')
+          assert_equal("AUTH PLAIN #{credential}\r\n", sock.gets)
+          sock.puts "235 2.7.0 Authentication successful\r\n"
         end
+        assert_equal("QUIT\r\n", sock.gets)
+        sock.puts "221 2.0.0 Bye\r\n"
+        sock.close
+        servers.each(&:close)
       end
+      port = servers[0].local_address.ip_port
+      return port
     end
   end
 end