The postal service is encouraging its 150,000 staff to take part in the annual campaign that sees men growing moustaches for the month of November in aid of the charity, the Institute of Cancer Research and the Movember Foundation.
Movember postmarks will be stamped onto letters for two weeks from today and for two weeks in November.
Prostate Cancer UK said it was not putting a figure on the amount it expected Royal Mail to raise for Movember, but the two-year partnership is expected to make at least £2m for the charity overall. The target for employees is £1m, which the company has pledged to match.
Owen Sharp, chief executive of Prostate Cancer UK, said: "We are delighted that Royal Mail is appealing to its employees to get involved in Movember.
"Even though on the surface it appears to be a fun initiative, it has been hugely successful not only in raising millions of pounds for research into prostate cancer, but also in managing to get younger men to start thinking about their health. We encourage men of all ages and all walks of life to get on board and grow a Mo this Movember."
Last year, the campaign raised £19.6m in the UK and £79.3m worldwide for prostate cancer charities.
Prostate Cancer UK was chosen as Royal Mail’s main charity partner after a vote by staff earlier this year.
Moya Greene, chief executive of the Royal Mail Group, said: "We have a proud history of charitable fundraising at Royal Mail. I am very confident that we will continue that tradition by raising funds during Movember and in the year ahead."
Neil Stuke from the BBC1 drama Silk, who plays a character with prostate cancer, launched Royal Mail’s support for Movember.