I've been playing around with a great new software tool that I've found especially helpful in tracking my @Waiting For emails.
It's called MSGTAG Status. It tags all my outgoing emails and sends me a confirmation when it is read. Unlike Outlook, it does not deliver a pop up screen to the recipient.
Also, rather than sending me an email receipt, it has a neat digital dashboard that allows me to track which emails have been read and which haven't.
In the past I would enter an @Waiting For task whenever I sent an email that required a response. Now I just pull up the dashboard and can tell at a glance where the open loops are. Brilliant!