It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Ruby 3.1 extracts some gems to bundled one, which requires to add these gems to Gemfile explicitly.
`net/smtp` is one of them, which affected Action Mailbox bug report templates.

* Steps to reproduce

Install `ruby 3.1.0dev`

```
git clone https://github.com/rails/rails.git
cd rails/guides
ruby bug_report_templates/action_mailbox_gem.rb
ruby bug_report_templates/action_mailbox_main.rb
```

* This commit addresses the following error `cannot load such file -- net/smtp (LoadError)`

```
$ ruby bug_report_templates/action_mailbox_gem.rb
... snip ...
Using rails 6.1.0
/home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require': cannot load such file -- net/smtp (LoadError)
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `block in require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:299:in `load_dependency'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/mail-2.7.1/lib/mail.rb:9:in `<module:Mail>'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/mail-2.7.1/lib/mail.rb:3:in `<top (required)>'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `block in require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:299:in `load_dependency'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/actionmailbox-6.1.0/lib/action_mailbox/mail_ext.rb:3:in `<top (required)>'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `block in require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:299:in `load_dependency'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/actionmailbox-6.1.0/lib/action_mailbox.rb:3:in `<top (required)>'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `block in require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:299:in `load_dependency'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/actionmailbox-6.1.0/lib/action_mailbox/engine.rb:9:in `<top (required)>'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `block in require'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:299:in `load_dependency'
	from /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/gems/3.1.0/gems/activesupport-6.1.0/lib/active_support/dependencies.rb:332:in `require'
	from bug_report_templates/action_mailbox_gem.rb:17:in `<main>'
```

* Added comment when this dependency can be removed based on https://bugs.ruby-lang.org/issues/17873

Refer
ruby/ruby#4530
rails#42308

Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Add net-smtp as a dependency for Ruby 3.1 compatibility

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Also add net-imap and net-pop to the gemspec

JRuby already has prerelease support for `io-wait` as a gem, and an
almost ready PR to also support `strscan` as a gem, dependencies
introduced by this change. Adding both to the Gemfile gets `bundle
install` to succeed, although specs fail later because Bundler does not
seem to support pointing to a java extension gem through git.

Add net-smtp as a dependency for Ruby 3.1 compatibility

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Also add net-imap and net-pop to the gemspec

JRuby already has prerelease support for `io-wait` as a gem, and an
almost ready PR to also support `strscan` as a gem, dependencies
introduced by this change. Adding both to the Gemfile gets `bundle
install` to succeed, although specs fail later because Bundler does not
seem to support pointing to a java extension gem through git.

Add net-smtp as a dependency for Ruby 3.1 compatibility

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Also add net-imap and net-pop to the gemspec

JRuby already has prerelease support for `io-wait` as a gem, and an
almost ready PR to also support `strscan` as a gem, dependencies
introduced by this change. Adding both to the Gemfile gets `bundle
install` to succeed, although specs fail later because Bundler does not
seem to support pointing to a java extension gem through git.

Add net-smtp as a dependency for Ruby 3.1 compatibility

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Also add net-imap and net-pop to the gemspec

This dependencies introduces `io-wait` and `strscan` as subdependencies,
but JRuby only has prerelease support for those. Make sure those
prereleases are properly picked up by our tests by adding them to the
`Gemfile`.

Add net-smtp as a dependency for Ruby 3.1 compatibility

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Also add net-imap and net-pop to the gemspec

This dependencies introduces `io-wait` and `strscan` as subdependencies,
but JRuby only has prerelease support for those. Make sure those
prereleases are properly picked up by our tests by adding them to the
`Gemfile`.

Add net-smtp as a dependency for Ruby 3.1 compatibility

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Also add net-imap and net-pop to the gemspec

This dependencies introduces `io-wait` and `strscan` as subdependencies,
but JRuby only has prerelease support for those. Make sure those
prereleases are properly picked up by our tests by adding them to the
`Gemfile`.

Add net-smtp as a dependency for Ruby 3.1 compatibility

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Also add net-imap and net-pop to the gemspec

This dependencies introduces `strscan` as a subdependency, but JRuby
only has prerelease support for it. Make sure the prerelease is
properly picked up by our tests by adding it to the `Gemfile`.

Add net-smtp as a dependency for Ruby 3.1 compatibility

It was recently removed from the default gems:

  - https://bugs.ruby-lang.org/issues/17873
  - ruby/ruby#4530

Also add net-imap and net-pop to the gemspec

This dependencies introduces `strscan` as a subdependency, but JRuby
only has prerelease support for it. Make sure the prerelease is
properly picked up by our tests by adding it to the `Gemfile`.