To make things clear I’m not writing about deleting an iCloud email account from an iOS device or Mac, but deleting the whole account altogether. Look here for removing an iCloud email account from a device without deleting the account. Read on for how to delete an iCloud email account altogether.
iCloud accounts are the email address used as the Apple ID for Apple services like iTunes Store or iOS App Store. Deleting an iCloud account would mean a user cannot login anymore and purchased items like movies, TV shows, eBooks and apps for iOS and macOS wouldn’t be accessible anymore as well.
Deleting an iCloud email account wasn’t possible in the past but has been made available by Apple in May of 2018 to support the European General Data Protection Regulation (GDPR). This is mandatory for users in Europe, but Apple thankfully implemented those features for users world-wide.
There are many options to manage an iCloud email address. Make sure to pick the right for your problem.