Hi, leroydouglas, your response was quite helpful. I did check out the first 2 links before and found that they don't work (probably because I am using Lion and the instructions seem to be SnowLeopard or even Leopard looking at the date of the articles).
However, the third actually sent me to a service available on the internet, and I have signed up for the service in trial mode, and sent a test e-mail to my girlfriend. The read confirmation came in a couple of seconds after she opened the mail ... this is exactly what I was hoping to achieve. I will check out further what the conditions are (fees etc.) to have this service available on a prolonged basis ... in any case, thanks alot.
Do you know if SMS delivery reports are possible in iPhone ? I found some tips on certain providers to add certain code to an SMS to trigger delivery reports, but my provider (Mobistar in Belgium) is not in that list. Strange, since from a simple Nokia (old model, not smartphone), delivery receipts on the same provider work fine ...