Setting up Devise with a custom mailer to send different confirmation emails based on devise scope.

confirmation_instructions_tenants.html.erb

# doki_core/mailer/confirmation_instructions_tenants.html.erb

I get sent to Tenants when requesting confirmation.

confirmation_instructions_users.html.erb

# doki_core/mailer/confirmation_instructions_users.html.erb

I get sent to Users when requesting confirmation.

devise.rb

# config/initializers/devise.rb

Devise.setup do |config|
  config.mailer = 'DokiCore::DeviseMailer'
end

devise_mailer.rb

# doki_core/app/mailers/devise_mailer.rb

module DokiCore
  class DeviseMailer < Devise::Mailer

    def confirmation_instructions(record, token, opts={})
      @token = token

      scope_name = Devise::Mapping.find_scope!(record)
      devise_mapping = Devise.mappings[scope_name]
      template = "confirmation_instructions_#{devise_mapping.scoped_path}".to_sym

      # set the template path to whereever you want templates to live.
      # defaults to [#{devise_mapping}/mailer, devise/mailer] but in this case
      # all the confirmation templates are in my main engine's mailer directory
      opts = {
        template_path: 'doki_core/mailer'
      }.merge(opts)

      devise_mail(record, template, opts)
    end

  end
end

routes.rb

# Super simplfied routing. Actual devise mounts are quite a bit 
# more complex and :users are scoped to a subdomain.

DokiCore::Engine.routes.draw do
  
  # User devise routes
  devise_for :users, class_name: 'DokiCore::User'
  
  # Tenant devise routes
  devise_for :tenants, class_name: 'DokiCore::Tenant',
  
end