Preview ActionMailer email content

(1) Assuming you already have a mailer action. E.g.

class NotificationMailer < ApplicationMailer

  def changed_password(email)
    mail(to: email, subject: 'Password Changed')
  end

end

(2) Create a preview at /spec/mailers/previews/notification_mailer_preview.rb E.g.

class NotificationMailerPreview < ActionMailer::Preview

  def changed_password
    NotificationMailer.changed_password('email')
  end
  
end