I don't doubt the OP but I'd like to add that, at times, Carnival customers can receive odd looking emails that are legit.
Yesterday I received an email from a different Carnival address that had to do with a reward I applied for requesting that the reward be used on an upcoming cruise. The email contained codes and jargon I had never seen before.
Another time earlier this year I got a weird looking email from an internal department at Carnival advising me that the cabin I booked for an upcoming cruise was going to be out of service that cruise and I being reassigned, and upgraded, to a balcony on the same deck.
The moral of the story is, as others have said, take no action on suspicious emails without first contacting Carnival yourself directly.