This is VERY obnoxious!!!!!
I read an email, then I want to flag it (only have red option, which sucks). Once I open an email, and decide I want to put a flag on it, I get an error message, that I can't flag it, since it had been opened/read. Then I have to delete about 10 messages, before Outlook "forgets" that rule, and then I can go back and flag it. A decade of more ago, We could flag emails after we opened them, and this horrible "rule" makes me angry every time I use Outlook. And, it is a hge waste of time. Think about it: How do I know that I want to "flag" something, until I open and read it. Then when I do, I have to waste a ton of time, deleting, and going back to flag it. UGH!!!!!