804 Hashtag

I think whatever I think of about digital technology might most likely be already realized in somewhere, but this is not about technology. This is about business tools. We must see a lot of, tons of emails every day. How about, all the emails in our business lives should be labeled with one or more hashtags before being sent to the recipient? It's nothing tricky. All we have to do is to put some hashtags on the email we are about to send, such as "project silver" tag and "not so urgent" or "you mush reply" or "it's a good news". etc. Your Gmail or Outlook will show the subject, date, sender, attached file, or size, but before everything the hashtags (in a very lean and smart way I'd like to imagine) so that you will be certainly able and comfortable to prioritize every single email you get. I'm sure it's not technology but protocol.