mailer_v2.rb

class BaseUserMailer
  
  def initialize(smtp_settings)
    @client = MailSendingLibrary.new(smtp_settings)
  end
  
  def send_mail(user, mail)
    @client.send_mail(user.email, mail.body)
  end
end

class TransactionalMailer <  BaseUserMailer
  
  SMTP_SETTINGS = ...
  
  def initialize()
    super(SMTP_SETTINGS)
  end
end

class MarketingMailer <  BaseUserMailer
  
  SMTP_SETTINGS = ...
  
  def initialize()
    super(SMTP_SETTINGS)
  end
end