Unable to remove action_mailbox

I'm using Ruby 3.0.3 + Rails 6.1.4. I tried to remove action_mailbox (and any unused railties) and have the following in my application.rb

%w(
  action_controller/railtie
  action_view/railtie
  active_job/railtie
  sprockets/railtie
).each do |railtie|
  begin
    require railtie
  rescue LoadError
  end
end

I also commented out any action_mailbox related configs.

Here's the Gemfile

# gem 'rails', '~> 6.1', '>= 6.1.4' # note this is commented out. I know it's overkill, but this didn't work
gem 'actionpack', '~> 6.1', '>= 6.1.4'
gem 'actionview', '~> 6.1', '>= 6.1.4'
gem 'activesupport', '~> 6.1', '>= 6.1.4'
gem 'railties', '~> 6.1', '>= 6.1.4'
gem 'sprockets-rails', '~> 3.4', '>= 3.4.1'

However, when I run bundle exec derailed bundle:mem, I still see action_mailbox

  rails/all: 62.25 MiB
    action_mailbox/engine: 33.3594 MiB
      action_mailbox: 33.3281 MiB
        action_mailbox/mail_ext: 33.2969 MiB
          action_mailbox/mail_ext/address_equality.rb: 31.9375 MiB
            mail/elements/address: 31.9375 MiB
              mail/parsers/address_lists_parser: 31.9063 MiB (Also required by: mail/parsers)
                mail/parsers: 1.7656 MiB
                  mail/parsers/received_parser: 1.1875 MiB

I don't think any Gems are depending on it, but is there a way that I can find out?

I tried running bundle exec gem dependency -R but I'm not sure if it's very helpful:

Gem actionmailbox-6.1.4
  actionpack (= 6.1.4)
  activejob (= 6.1.4)
  activerecord (= 6.1.4)
  activestorage (= 6.1.4)
  activesupport (= 6.1.4)
  mail (>= 2.7.1)
  Used by
    rails-6.1.4 (actionmailbox (= 6.1.4))

Gem rails-6.1.4
  actioncable (= 6.1.4)
  actionmailbox (= 6.1.4)
  actionmailer (= 6.1.4)
  actionpack (= 6.1.4)
  actiontext (= 6.1.4)
  actionview (= 6.1.4)
  activejob (= 6.1.4)
  activemodel (= 6.1.4)
  activerecord (= 6.1.4)
  activestorage (= 6.1.4)
  activesupport (= 6.1.4)
  bundler (>= 1.15.0)
  railties (= 6.1.4)
  sprockets-rails (>= 2.0.0)