Adding a second iCloud email account to Mail.app in macOS Sierra How to add a second additional email iCloud account in Mail.app?

I am helping someone who ended up with two separate iCloud accounts. One is hooked up to his new MacBook Pro, no problem. Email, Messages, Reminders, Notes, and such all syncing.

Now this person wants to access the email for the second iCloud/Mac.com/Me.com account. Need just email, no other iCloud features such as Messages, Reminders, Notes, and so on.

How to add an additional iCloud account for email only? 

I am afraid to use System Preferences > Accounts > iCloud item in list as that might totally confuse and ruin the already-assigned account for all the syncing. We want to add a second email, not replace the already-assigned iCloud account.
Go to the mail app and open mail preferences. Then, under accounts, hit the + button. Select "iCloud" and input the log-in information. Select ONLY the mail icon. Then hit "Add Account".

By going through the mail app preferences instead of System Preferences you can avoid dealing with all of the iCloud options. Here is a picture of what it looked like when I added a second iCloud mail account. On the left side in the list of accounts you can see two iCloud icons (boxed in red):