Voting by mail can be convenient, but you have to PLAN AHEAD. You must register to vote before you can vote by mail. Generally, voting by mail is done early, before Election Day. Some states, such as Oregon, conduct elections primarily by mail. But in most states, you have to request an absentee ballot, sometimes up to three months before Election Day. In other states you can only vote by mail under special circumstances, such as an illness or an overseas assignment which precludes voting in person. Check the rules in your state below: