I don't even use iCloud myself, if that's the cause. If Apple doesn't support POP anymore then fine, state it to everyone, so we can move on. HOWEVER, that still leaves two major issues. One, for people who still want or need to access older email content when traveling or outside an internet zone how is this possible? Two, if the Apple Mail app doesn't do this then you are pushing your customers to download 3rd party apps to do a job that should be the most basic thing on a smartphone. The workarounds I've read about including copy and paste email content to your notes or archive the email before it disappears are stupid.
I take photos with my phone and they sit there for as long as I decide to keep them, regardless of internet connection. Why is it so hard, or so bad, or outdated to want a tiny sized text file to stay in my email until I don't need it anymore?