Business Minister Michael Fallon said the aim was to give as many of Britain's postal workers as possible a chance to own a stake in their company.
The announcement was made ahead of a special two-day conference when Communication Workers Union leaders will decide whether to hold a strike ballot over pay, jobs and other issues linked to the controversial sell-off.
Ministers said they were eager for the postmen and women who have worked hard in turning Royal Mail around to get access to free shares so that they have a "real stake" in the company.
Under automatic enrolment, as many employees as possible will be encouraged to benefit from free shares in the company as well as given the opportunity to opt out if they choose, said Mr Fallon, adding: "Postmen and postwomen are at the very heart of Royal Mail making sure that post is delivered to all parts of the country, whatever the season.
"They are absolutely central to the future of the company and so it's important that they share in its success, as decided by Parliament two years ago.
"This is a unique opportunity for our nation's dedicated postmen and women to own a real and meaningful stake in their company. Owning shares will mean that they get regular dividends and have the power to vote on company matters like any other shareholder."