By Julianne Pepitone, NBC News

(NBC News) - If you bought an Amazon Kindle e-book between April 2010 and May 2012, check your inbox — you may have money coming to you.

Early Tuesday, Amazon sent emails to customers who are eligible for a new e-book refund: "Good news! You are entitled to a credit of $[amount] for some of your past Kindle book purchases."

It's also good news for Amazon, as publishers were forced to issue the refunds as part of settlements in an e-book price-fixing case that allegedly targeted Amazon.

Amazon sent emails to customers who are eligible for a new e-book refund.

The drama began in April 2012, when the Department of Justice sued Apple and five major publishers, alleging they colluded to keep the price of e-books artificially high. State attorneys general and class plaintiffs also filed suit.

The lawsuits alleged a conspiracy: Booksellers didn't like the discounted e-book price structure Amazon launched in 2007, in which the company sold many titles for $9.99. So just before Apple introduced the iPad in January 2010, the suits alleged, the publishers went to Apple in an effort to force Amazon to hike e-book prices. Amazon did raise prices a few days after the iPad was unveiled.

The price-fixing case wore on over the next year-and-a-half. Eventually, in December 2013, a federal court approved settlements reached with publishers Hachette, HarperCollins, Simon & Schuster, Macmillan and Penguin.

The credits are a result of those settlements. Eligible customers don't need to do anything — Amazon has already applied the amount to their accounts. Available credit will automatically be applied to customers' next purchase of a Kindle e-book or a print book sold by

Don't wait too long to use that refund, though. The credit expires after March 31, 2015.