You have a major, major flaw in your Contacts function/feature.

If I send an email to a existing contact who has a new email address, Yahoo DOES NOT SAVE the new address! It is not until the recipient REPLIES to my email that the system saves the new address!
I just found this out after a long interaction with a Help desk person - who also didn't know this!

People change email addresses all the time. And frequently have more than one valid email address for various reasons. Yahoo's inability to record address changes or new addresses is a major flaw.
Nobody has time to sit online for nearly an hour while the Help desk researches this issue. I think that Yahoo has a responsibility to its users to provide the key instructions about how to update or change email addresses for existing contacts. But you failed to do so, not only to me a user, but also to your help desk people!.
Very, very disappointing, Yahoo!
I've been your devoted user for a number of years, through a number of hiccups and issues. I am angry that you would fail in such a key way and force us to figure out the solution for ourselves! The New Yahoo Mail is not new any longer - and this should have been fixed a long time ago!