Postal workers around the country began delivering 2.9 million information packs to registered voters on Thursday.
The packs include an Easy Vote card, which people can take with them to polling booths.
Chief Electoral Officer Robert Peden said each card has voter information that will help staff at polling booths issue ballot papers.
He said the mailout is bigger than the one for the last election, which involved 2.8 million packs.
Mr Peden said about 188,000 eligible voters are still not enrolled, including about 85,000 between the ages of 18 and 24.
People are able to enrol until 7 November, the day before the election.
