在Rails3/ActionMailer中设置Message-ID邮件头

class MyMailer< ActionMailer::Base
  default from: "noreply@example.com"

  def sample_email(to_email)
    mail(to: to_email, subject: "Sample Email") do |format|
      format.text { render plain: "This is a sample email." }
    end

    # 在邮件发送时添加自定义的Message-ID
    self.message_id = "custom_message_id@example.com"
  end
end