To access the McDVoice survey via mail, look for a unique survey code on your McDonald's receipt. This code allows you to participate in the McDVoice survey, which is designed to gather feedback on your recent dining experience. Visit the website mcdvoice.com survey and enter the survey code as instructed. If you received a physical invitation with a survey code, follow the included instructions to complete the survey. By sharing your opinions, you can help McDonald's improve their services and products. As a thank you, you may receive a coupon or offer for your next visit.