This should be done using Yahoo Messenger SDK. It is a C++ and JavaScript API. If you know C++ and JavaScript, you are probably capable to do it. Check [login to view URL] for more info.
Description:
All you have to do, is intercept the user friend's list, get his emails and check if these emails are on my website using a "POST".
According to my website response, you will show a correspondent image and message.
Also, update the status of the user.
If you find a way to message the user friend's and update the Y profile and the user email you will receive a bonus.
Easy enough, isn't?