It is unknown how many emails Apple sent out, or to whom, but from the generalized wording it seems like the company is delivering the correspondence to a large swath of iTunes account holders. More specifically, the emails are apparently targeted at users who recently made in-app purchases.
From Apple's letter:
Dear iTunes account owner,
Apple is committed to providing parents and kids with a great experience on the App Store. We review all app content before allowing it on our store, provide a wide range of age-appropriate content, and include parental controls in iOS to make it easy for parents to restrict or disable access to content.
We've heard from some customers that it was too easy for their kids to make in-app purchases. As a result, we've improved controls for parents so they can better manage their children's purchases, or restrict them entirely. Additionally, we are offering refunds in certain cases.
The email goes on to note that if some in-app purchases happened to be made without parental consent, users may request a refund by filling out a form. The company will review the request and respond via email when a decision has been made.
In January, Apple reached a settlement with the U.S. Federal Trade Commission in which the company agreed to modify the in-app purchase process to ensure each purchase was expressly authorized by the consumer. The company also earmarked $32.5 million for refunds. Earlier this month, Apple had yet to introduce the promised changes as a Mar. 31 deadline looms.
The issue stems from the in-app purchasing system, which made it too easy for children to rack up enormous real world bills after buying virtual game currency. The FTC announced in early 2011 that it would investigate iTunes' in-app purchasing system after receiving complaints from consumers.
At the time, Apple's method employed a time-sensitive lock window in which a user can enter a password to buy in-app content and make additional purchases without re-entering their pass phrase.
Those who have not yet received the email can sign in to iTunes to review past purchases, and if a discrepancy is found, use a special link to request a refund. All requests must be submitted by Apr. 15, 2015.