The release date for Harry Potter and the Deathly Hallows remains unconfirmed, but the postal service is to meet online retailers next month to chart out the plans well ahead of the release.
Demand is expected to be as high as last year when 500,000 pre-ordered copies of the sixth book were delivered in the UK.
"This kind of operation takes a lot of planning," A Royal Mail spokesman was quoted by the BBC, as saying.
A Harry Potter book release is one of the busiest times of the year for postal workers, next to Christmas.
JK Rowling said recently that she was close to finishing the final book in the series but would not reveal any plot details.
However the author has admitted two characters will die.
Royal Mail expects to deliver hundreds of thousands of copies
This has sparked speculation amongst fans who think one of them could be Harry Potter himself.
The first four novels in the series, based around a young wizard and his friends, have been turned into films.
The fifth, Harry Potter and the Order of the Phoenix, is currently in production and is due to be released in UK cinemas on 13 July.
Helena Bonham Carter joins the cast as the evil Bellatrix Lestrange and Imelda Staunton will play the part of dark arts teacher Dolores Umbridge.