Your Apple ID was used to sign in to iCloud on an iPhone 5

I’m getting emails saying that my Apple ID was used to sign into an iPhone 5 and an iPad Pro 12.9 1st generation. The email addy that is given is an old addy of mine that has been defunct for over 15 years! I’ve seen two other posts that mention an iPhone 5 but can’t access the posts and they both are unsolved. I do not have either one of said devices. I’m starting to think it’s a phishing email, but the emails have an Apple certificate.