diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 740f4b2..ca2769a 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -486,6 +486,7 @@ def debug_output=(arg)
 
     #
     # :call-seq:
+    #  start(address, port = nil, helo: 'localhost', auth: nil, tls: false, starttls: :auto, tls_verify: true, tls_hostname: nil, ssl_context_params: nil) { |smtp| ... }
     #  start(address, port = nil, helo: 'localhost', user: nil, secret: nil, authtype: nil, tls: false, starttls: :auto, tls_verify: true, tls_hostname: nil, ssl_context_params: nil) { |smtp| ... }
     #  start(address, port = nil, helo = 'localhost', user = nil, secret = nil, authtype = nil) { |smtp| ... }
     #
@@ -552,6 +553,7 @@ def debug_output=(arg)
     #
     def SMTP.start(address, port = nil, *args, helo: nil,
                    user: nil, secret: nil, password: nil, authtype: nil,
+                   auth: nil,
                    tls: false, starttls: :auto,
                    tls_verify: true, tls_hostname: nil, ssl_context_params: nil,
                    &block)
@@ -560,7 +562,7 @@ def SMTP.start(address, port = nil, *args, helo: nil,
       user ||= args[1]
       secret ||= password || args[2]
       authtype ||= args[3]
-      new(address, port, tls: tls, starttls: starttls, tls_verify: tls_verify, tls_hostname: tls_hostname, ssl_context_params: ssl_context_params).start(helo: helo, user: user, secret: secret, authtype: authtype, &block)
+      new(address, port, tls: tls, starttls: starttls, tls_verify: tls_verify, tls_hostname: tls_hostname, ssl_context_params: ssl_context_params).start(helo: helo, user: user, secret: secret, authtype: authtype, auth: auth, &block)
     end
 
     # +true+ if the SMTP session has been started.
@@ -572,6 +574,7 @@ def started?
     # :call-seq:
     #  start(helo: 'localhost', user: nil, secret: nil, authtype: nil) { |smtp| ... }
     #  start(helo = 'localhost', user = nil, secret = nil, authtype = nil) { |smtp| ... }
+    #  start(helo = 'localhost', authtype: nil, auth: {...}) { |smtp| ... }
     #
     # Opens a TCP connection and starts the SMTP session.
     #
@@ -580,11 +583,10 @@ def started?
     # +helo+ is the _HELO_ _domain_ that you'll dispatch mails from; see
     # the discussion in the overview notes.
     #
-    # If both of +user+ and +secret+ are given, SMTP authentication
-    # will be attempted using the AUTH command.  +authtype+ specifies
-    # the type of authentication to attempt; it must be one of
-    # :login, :plain, and :cram_md5.  See the notes on SMTP Authentication
-    # in the overview.
+    # If either +auth+ or +user+ and +secret+ are given, SMTP authentication
+    # will be attempted using the AUTH command.  +authtype+ specifies the type
+    # of authentication to attempt; it must be one of :login, :plain, and
+    # :cram_md5.  See the notes on SMTP Authentication in the overview.
     #
     # === Block Usage
     #
@@ -623,12 +625,14 @@ def started?
     # * Net::ReadTimeout
     # * IOError
     #
-    def start(*args, helo: nil, user: nil, secret: nil, password: nil, authtype: nil)
+    def start(*args, helo: nil,
+              user: nil, secret: nil, password: nil, authtype: nil, auth: 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]
+      auth ||= [user, secret, authtype] if user || secret
       if defined?(OpenSSL::VERSION)
         ssl_context_params = @ssl_context_params || {}
         unless ssl_context_params.has_key?(:verify_mode)
@@ -643,13 +647,13 @@ def start(*args, helo: nil, user: nil, secret: nil, password: nil, authtype: nil
       end
       if block_given?
         begin
-          do_start helo, user, secret, authtype
+          do_start helo, user, secret, authtype, auth
           return yield(self)
         ensure
           do_finish
         end
       else
-        do_start helo, user, secret, authtype
+        do_start helo, user, secret, authtype, auth
         return self
       end
     end
@@ -667,7 +671,8 @@ def tcp_socket(address, port)
       TCPSocket.open address, port
     end
 
-    def do_start(helo_domain, user, secret, authtype)
+    def do_start(helo_domain, user, secret, authtype, auth = nil)
+      # pp({method: __method__, user:, secret:, authtype:, auth:}.compact)
       raise IOError, 'SMTP session already started' if @started
       s = Timeout.timeout(@open_timeout, Net::OpenTimeout) do
         tcp_socket(@address, @port)