Fixed issue sending emails to unaffected recipients on 53x error

When multiple recipients were specified and one recipient encountered
a 53x error, despite an exception being raised, emails were being sent
to the recipients that didn't encounter errors. This patch has been
applied to handle 53x errors the same way as other errors.

lib/net/smtp.rb

@@ -906,23 +906,10 @@ def mailfrom(from_addr, require_smtputf8 = false)
 
     def rcptto_list(to_addrs)
       raise ArgumentError, 'mail destination not given' if to_addrs.empty?
-      ok_users = []
-      unknown_users = []
       to_addrs.flatten.each do |addr|
-        begin
-          rcptto addr
-        rescue SMTPAuthenticationError
-          unknown_users << addr.to_s.dump
-        else
-          ok_users << addr
-        end
-      end
-      raise ArgumentError, 'mail destination not given' if ok_users.empty?
-      ret = yield
-      unless unknown_users.empty?
-        raise SMTPAuthenticationError, "failed to deliver for #{unknown_users.join(', ')}"
+        rcptto addr
       end
-      ret
+      yield
     end
 
     # +to_addr+ is +String+ or +Net::SMTP::Address+