3GS yahoo email issue

[jikserman]

I've had my iphone for 3 weeks now. I have yahoo set up to deliver emails to the phone obviously. Problem i'm having is every 3-4 days all the emails that i've "deleted" return back into my inbox and sent bins. Not sure what i'm doing wrong. Its become very confusing, especially with a company that gets 70-100 emails a day. Thought it was an issue with push and fetch emails, but i've tried it with both settings and it still does it. Any suggestions on what to try?