gem 'unsubscribe'

$ bundle

$ gem install unsubscribe

rails g unsubscribe:install
rails unsubscribe:install:migrations
rails db:migrate

class User < ApplicationRecord
  include Unsubscribe::Owner
end

User.first.mailer_subscriptions
# => #<ActiveRecord::Associations::CollectionProxy [#<Unsubscribe::MailerSubscription>, #<Unsubscribe::MailerSubscription>] >

User.first.subscribed_to_mailer? "MarketingMailer"
# => true/false

User.first.to_sgid_for_mailer_subscription
# => #<SignedGlobalID:123 ...>

class MarketingMailer < ApplicationMailer  
  include Unsubscribe::Mailer

  unsubscribe_settings name: "Marketing Emails", description: "Updates on promotions and sales."

  def promotion
    mail to: @recipient.email
  end  
end

  MarketingMailer.with(
    recipient: User.first
  ).promotion.deliver_now

Unsubscribe::MailerSubscription.first.action
# => "Unsubscribe from"/"Subscribe to"

Unsubscribe::MailerSubscription.first.call_to_action
# => "Unsubscribe from Marketing Emails"/"Subscribe to Marketing Emails"

Unsubscribe::MailerSubscription.first.description
# => "Updates on promotions and sales."

Unsubscribe::MailerSubscription.first.name
# => "Marketing Emails"

<%= link_to "Unsubscribe", @unsubscribe_url %>

# config/locales/en.yml
en:
  unsubscribe:
    action:
      subscribe: "Subscribe to"
      unsubscribe: "Unsubscribe from"

bin/rails test
bundle exec standardrb