How can I know if an email address is legitimate?

It could be. Generally, Apple emails end in Apple.com but you need to make sure that the apple.com is the actual from email address, not just the visible name. Right-click on the email address or two-finger click on it to see the delivery email address.

And, see Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

That is a scam apple I receive a lot of Apple ID emails from apple and I have never seen that address