Cannot get mail - the connection to the server failed
iPhone 6S+, iOS 10.3.1
I use the Outlook app as my email client (works great). I had removed the native Apple mail app, but recently I found a need for it and I want to use my icloud.com email address with it, which is different from my Apple ID, but my icloud.com email address is visible under my profile on icloud.com. I CAN see emails to my icloud.com email address under the "Mail" section on the website icloud.com.
However, I cannot receive or send emails from the native Apple email app, which is set up to use my icloud.com email address. It just keeps saying, "Cannot get mail - the connection to the server failed".
Help?