Issue #20065 has been updated by deivid (David RodrÃguez). I created https://github.com/ruby/ruby/pull/9234 to fix this! ---------------------------------------- Bug #20065: cannot require "net/smtp" with Ruby3.3.0-rc1 and bundler 2.5.0.dev https://bugs.ruby-lang.org/issues/20065#change-105677 * Author: s3fxn (s3 fxn) * Status: Open * Priority: Normal * ruby -v: 3.3.0-rc1 * Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- $ ruby -v ruby 3.3.0rc1 (2023-12-11 master a49643340e) [x86_64-linux] $ bundle -v Bundler version 2.5.0.dev $ bundle init $ bundle add net-smtp $ bundle exec ruby -e 'require "net/smtp"' -e:1: warning: net/smtp was loaded from the standard library, but is not part of the default gems since Ruby 3.1.0. Add net-smtp to your Gemfile or gemspec. $ tail -1 Gemfile gem "net-smtp", "~> 0.4.0" -- https://bugs.ruby-lang.org/