Sounds like you have it setup in Exchange and Regular mail. Try removing the regular one, but leave the exchange setup (so you can use gmail push). visit this link for proper gmail setup on an iphone, and it will also sync your contacts, calender and along with mail... Google Sync for your phone

no one knows?

I ask this question for my friend may need this. Please read the passage as follows:
On my iPhone 4 I have 4 email accounts.....2 GMail and 2 Bigpond.
The BigPond ones have less files. You download and then delete. ONCE.
They always download again on my PC once, exactly what I need.

The Gmail accounts, on the iPhone download into Inbox, then after deletion, they download again into All Mail. They also download and go to Sent file all the emails I sent on my PC.

Then I have to download and delete them a 2nd time from Sent and /or All Mail.

Is there some way to get Gmail to download to the iPhone just once the ones I read only on my iPhone, instead of the stuff already read on my PC.
Conversely, the stuff I've read on my PC downloads again to the iPhone,

Any simple way to simplify all this?
Thank u soo much for your help.