diff --git a/NEWS.md b/NEWS.md
index 4638fac..63a324b 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,10 +1,25 @@
 # NEWS
 
-## Version 0.4.0
+## Version 0.4.0 (2023-09-20)
 
-*  add Net::SMTP::Authenticator class and auth_* methods are separated from the Net::SMTP class. <https://github.com/ruby/net-smtp/pull/53/files>
+### Improvements
+
+* add Net::SMTP::Authenticator class and auth_* methods are separated from the Net::SMTP class. <https://github.com/ruby/net-smtp/pull/53>
+      This allows you to add a new authentication method to Net::SMTP.
+      Create a class with an `auth` method that inherits Net::SMTP::Authenticator.
+      The `auth` method has two arguments, `user` and `secret`.
+      Send an instruction to the SMTP server by using the `continue` or `finish` method.
+      For more information, see lib/net/smtp/auto _*.rb.
+* Add SMTPUTF8 support <https://github.com/ruby/net-smtp/pull/49>
+
+### Fixes
+
+* Revert "Replace Timeout.timeout with socket timeout" <https://github.com/ruby/net-smtp/pull/51>
+* Fixed issue sending emails to unaffected recipients on 53x error <https://github.com/ruby/net-smtp/pull/56>
+
+### Others
 
-*  Add SMTPUTF8 support <https://github.com/ruby/net-smtp/pull/49>
+* Removed unnecessary Subversion keywords <https://github.com/ruby/net-smtp/pull/57>
 
 ## Version 0.3.3 (2022-10-29)
 
diff --git a/lib/net/smtp.rb b/lib/net/smtp.rb
index 46f2314..6ceb61b 100644
--- a/lib/net/smtp.rb
+++ b/lib/net/smtp.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 # = net/smtp.rb
 #
 # Copyright (c) 1999-2007 Yukihiro Matsumoto.
@@ -22,7 +23,6 @@
 end
 
 module Net
-
   # Module mixed in to all SMTP error classes
   module SMTPError
     # This *class* is a module for backward compatibility.
@@ -36,7 +36,7 @@ def initialize(response, message: nil)
         @message = message
       else
         @response = nil
-        @message = message || response 
+        @message = message || response
       end
     end
 
@@ -187,7 +187,7 @@ class SMTPUnsupportedCommand < ProtocolError
   #                     user: 'Your Account', secret: 'Your Password', authtype: :cram_md5)
   #
   class SMTP < Protocol
-    VERSION = "0.3.3"
+    VERSION = "0.4.0"
 
     # The default SMTP port number, 25.
     def SMTP.default_port
@@ -210,7 +210,7 @@ class << self
 
     def SMTP.default_ssl_context(ssl_context_params = nil)
       context = OpenSSL::SSL::SSLContext.new
-      context.set_params(ssl_context_params ? ssl_context_params : {})
+      context.set_params(ssl_context_params || {})
       context
     end
 
@@ -281,7 +281,7 @@ def inspect
     attr_accessor :esmtp
 
     # +true+ if the SMTP object uses ESMTP (which it does by default).
-    alias :esmtp? :esmtp
+    alias esmtp? esmtp
 
     # true if server advertises STARTTLS.
     # You cannot get valid value before opening SMTP session.
@@ -829,8 +829,6 @@ def open_message_stream(from_addr, *to_addrs, &block)   # :yield: stream
     # Authentication
     #
 
-    public
-
     DEFAULT_AUTH_TYPE = :plain
 
     def authenticate(user, secret, authtype = DEFAULT_AUTH_TYPE)
@@ -1130,11 +1128,9 @@ def to_s
         @address
       end
     end
-
   end   # class SMTP
 
   SMTPSession = SMTP # :nodoc:
-
 end
 
 require_relative 'smtp/authenticator'
diff --git a/net-smtp.gemspec b/net-smtp.gemspec
index efc9b60..b19844f 100644
--- a/net-smtp.gemspec
+++ b/net-smtp.gemspec
@@ -22,11 +22,7 @@ Gem::Specification.new do |spec|
   spec.metadata["homepage_uri"] = spec.homepage
   spec.metadata["source_code_uri"] = spec.homepage
 
-  spec.files         = %w[
-    LICENSE.txt
-    lib/net/smtp.rb
-    net-smtp.gemspec
-  ]
+  spec.files = `git ls-files README.md NEWS.md LICENSE.txt lib`.split
   spec.require_paths = ["lib"]
 
   spec.add_dependency "net-protocol"