It preserves privacy by splitting the vote and the identification forms into two different envelopes. The vote (and only the vote) goes into a second envelope t

It preserves privacy by splitting the vote and the identification forms into two different envelopes. The vote (and only the vote) goes into a second envelope that is placed into the return envelope along with the identifying information. After the information is verified, the envelope with the vote is then added to a ballot box (and not opened right away). The whole process also happens in the open, so everyone interested in either the process or not trusting it to be properly done can stand by and watch. At least here postal votes are processed like this.