Suspicious email from Apple

I received 2 emails today that my appleID was used to sign into "Messages" on an iMac somewhere in USA or northern America. The sender of these emails seemed legit. So, a valid Apple address. Problem is, this emailaddress is definitely mine but I'm not registered with Apple on this emailaddress. It's a Gmail account which I use privately. I have an iCloud account for my apple id. I Checked my apple id settings and also there's no trace of any fallback (notification) emailaddress.

Is there anywhere you can report (suspicious) emails to Apple?

Really strange. I'll change my password of my icloud and Gmail account just to make sure. Both are 2FA so I guess I'm good.

Thanks for any feedback!