That may not matter that much, as even if you run a relatively strict policy about where you send the reply, you can still easily get bitten by external mistakes there: Because of the huge number of individually administered departments that might each become authorized recipient of such data, a malicious party only needs to find one suitably dangling DNS delegation to score a "…@attacker-controlled-subdomain.legitimate.example" mailbox. The sender would not be able to prevent this.. unless its regulatory oversight body is very patient about repeatedly delaying legitimate requests for seemingly-minuscule formal defects. (Mentioning just for context. Probably not the mechanism at play here, Revolut would have tried to shift blame in the press release if it was.)