The truths of religion are never so well understood as by those who have lost the power of reasoning.
— Voltaire, Dictionnaire philosophique (via philosophybits)
If you receive your ballot in the mail and want to avoid USPS uncertainty then drop off your ballot at a ballot drop off box or your local county elections office.
If you must return your ballot in the mail, the USPS recommends sending at least 1 week before Nov 3rd, but you should return it as early as you are possible to account for compounding USPS delays.
If you do not receive a ballot in the mail or you later change your mind to vote in person, then most states allow you to still vote in person!
Follow this guide to ensure the integrity of your vote and others, whether in-person or mail-in!
Plan your vote here with detailed information on your state regarding whether you can vote by mail, vote early in person, and more.
Axios has also put together a quick reference of voting methods and dates by state.
Another comprehensive list was put together regarding voting dates and deadlines, absentee rules, and answers to other frequent questions voters have, all in one place. Mobile friendly view here.