tl;dr: For those who applied for the $125 payout option in the Equifax data breach settlement, you should've gotten an email requiring that you provide more information by October 15, or that your claim would be denied.
The FTC confirms it's legit: https://www.ftc.gov/enforcement/cases-proceedings/refunds/eq... (FAQ 4 item 2)
The article's author says Gmail filed it into the 'Promotions' folder.