Well it’s been enabled for my accounts, finally, so the first thing I did was to see how I can flag items from my iPhone so that I may review at a more convenient time. No further: simply move the mail into the ‘Starred’ folder and you’re done. Granted, it also removes it from the Inbox view, but as far as I am concerned that is quite all right.

Now, if only Apple’s Mail wouldn’t display these IMAP accounts so weirdly. I am uncertain if it’s a mistake on my part or not, though my other IMAP accounts look just fine.