But there's no way you'll succeed in pushing people to reply to those requests you're making.
Mail to my inbox might be considered 'important' by the sender and might consider a header that makes my MUA ask me if I'd like to confirm that I'd read the message - but I can disagree and decline. In fact, I have rules that filter out important flags at work (they are always abused and there's no need to flag something on your side if I'm reasonably on top of my mail queue anyway) and ignore read receipts (Send me stuff and I read it unless it is spam. But I decide when and won't disclose that with anyone).
Use a good subject and accept that mail is not a real time protocol and we're getting along.
