About half of all Standard Life policyholders could gain a windfall of more than £1,000 if they support the company's plans to go public.
Standard Life hopes to scrap its once-cherished mutual status
The other half could see windfalls of between £500 and £1,000.
To demutualise, the Edinburgh-based insurer requires a 75% yes vote to approve the plan for its £5bn stock market flotation.
Standard Life is encouraging as many of its 2.4 million members as possible to vote, which they must do before 28 May.
Vote and proposal
Eligible members will receive 185 shares, which are expected to be worth between 240 and 290 pence, with the option of more shares depending on their policies.
The packs will be sent today to 2.4 million eligible members, as well as an additional 2.1 million policy holders.
The chief executive Sandie Crombie said that demutualisation was the best proposal that his members could consider:.
"We want to distribute the full stock market value of Standard Life to our 2.4 million members.
"We want to reduce the risks they face in running the business, and we want access to the markets to raise more capital to develop the business," he told the BBC.
Merrill Lynch and UBS, Standard Life's financial advisers, have valued the company at between £4.8bn and £5.5bn, including £1.1bn of new money which could be raised if it floats.
A special general meeting of Standard Life is planned on 31 May in Edinburgh, when members will be asked to vote on the proposal.
Even if voting members have sent their voting replies, they can still attend the meeting and vote in person.
A strong turnout in May is likely to be seen as a vote of confidence in management, including CEO Sandy Crombie, who announced the plans after a strategic review in 2004.
The Scottish insurer also revealed 2004 losses of £340m. But its profits last year were £152m, aided by 3,500 job cuts.
The insurer faces stiff competition in its sector and its 2005 UK sales were sluggish in comparison to sales at Friends Provident and Prudential.
Life insurance analyst Ned Cazalet said investors would want to see clear evidence that Standard Life was on track to turn itself around, since it was badly hit by a stock market fall between 2000 and 2003.
He said: "First of all, we need to understand the structure of the demutualisation, how much capital will be raised and what are the prospects for Standard Life in its reformed condition.
"Everything else is down to price, sentiment and execution."
The listing, expected in July if May's vote is positive, will also mark the end of an era for Britain's mutuals, most of which have been floated or were sold to listed firms to improve funding.
Standard Life shocked rivals and customers two years ago when it announced plans to go public.
The U-turn angered some members of the Scottish group, which only four years previously spent more than £10m in a campaign to preserve its mutual status. At that point, its value was estimated at up to £18bn.
Talking to the BBC, Fred Woollard, who led the failed attempt in 2000 to force Standard Life to demutualise, said: "I think it is very sad for all the policy holders that the value of the company has shrunk so badly in the last six years.
"The unfortunate reality is that Standard Life's management is only embracing demutualisation because they have destroyed most of the company's capital and need to go to the financial markets to raise another billion pounds or so."
The Edinburgh-based mutual insurer plans to request final approval for the change from the Court of Session in Scotland.
If the proposal is approved by the court and all legal requirements are met, demutualisation can go ahead.