I fought this problem for over 12 hours the other day....right in the middle of a busy work day....and got nothing else done. Apple was useless and Yahoo was useless as well. Had a phone plugged into each ear on tech support....and nothing! I just quit everything and chased it down myself.
But....I did come up with a work around.
Here is the problem: Many of us have Yahoo bizmail accounts with a domain and email addresses. I originally had a problem attaching to any of them with my new OS9.0.2 phone, but eventually could attach to the main yahoo address. That did me no good, as I don't use that address for anything; I use the email address that I created under that General Yahoo account. The only thing that comes into the general account is billing information from Yahoo and Whois information from the registry. Even when I programmed the phone exactly like my older iPhone 4S, it wouldn't attach to the sub-email that I created.
The problem is in OS 9.0.2
So....within your bizmail account (and this is hard to find) there is a way to set up a second email address and use it as a forwarding email. I used a gmail account, but just about any email service should work (mail.com, outlook.com, etc.). I can tell you that Gmail works. You will have to turn-on forwarding in your bizmail account. Once you have the gmail (or other) account set up in bizmail as a forwarding address, then just point your iPhone to that address.
Your computer will still retrieve mail the old way.
New email will come into your bizmail address and get forwarded, but a copy stays in bizmail to be retrieved by the computer.
Sent email will go out of your computer on bizmail as before.
Sent email will go out of your iPhone on Gmail.
An email sent to you will now show up on the computer and the iPhone using OS 9.0.2
Hope this helps....I wish I had someone tell me this, while I was having a nervous breakdown. I usually get 100 emails per day for business.