iphone 4s keeps "checking for email"

I've been searching for days to try and find a fix - I've returned my phone to apple and they exchanged it along with trying to work my problem over the phone and in a store. I'm reaching the end of my frustration rope and considering getting a different type of phone due to the issue.

I currently have 4 email address to my phone - 2 MSN (Hotmail set ups) 1 work (Server email) and 1 gmail account. My phone worked great for 6 months and then about 2 weeks ago would "check for email" constantly and drain my battery to dead. I have done the following to try and rectify the problem.

Reset settings

Restore phone from new

Restore from back up

Delete emails and re-install them

Hard reset from phone (This works for a minute but then locks up again and won't sync all email accounts)

Checked passwords - even changed them

Turned off mail waited then turned back on

Turned to airplane mode

Nothing works and Apple said they didn't know and hadn't heard of this ever happening. In reading the hundreds of articles that I've read over the last few days, nothing seems to rectify my problem.

Does anyone have any answers or solutions that seem to have worked or is anyone having this problem as well.

Thanks,