Rails track which User emails have received an email to avoid sending duplicate emails

Question

I'm working on creating a basic survey app to better learn Rails.

Right now I'm working on learning how to send emails. I've gotten it to work, but now I'm running into a scenario where I send out a lot of duplicate emails. The duplicates are coming out because I'm only checking for a status of Submitted on PUT and then sending out the email.

def update
    p params
    # unless signed_in?
    #   redirect_to signin_path
    # end
    respond_to do |format|
      if @survey.update(survey_params)
        @survey.check_email
        if @survey.status == "Submitted"
          SurveyMailer.survey_created(@survey).deliver
        end
        format.html { redirect_to @survey, notice: 'Survey was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @survey.errors, status: :unprocessable_entity }
      end
    end
  end

What's the best way to check/track which emails for a survey I've sent it out to? Basically some sort of "if user has not been notified that a survey has been shared with them, send it out, otherwise don't"