Emails keep re-downloading

Hey guys!
I have an iPhone 3G iOS 4.2.1. I noticed a couple of days ago that everytime I open the Mail app the emails are redownloaded... It's like the email accounts are empty and the phone downloads the emails... It's really annoying... It started all of the sudden.
I tried to delete my email accounts, restart the iPhone... But the same weird thing happens...
Any ideas?

miles01110 said:

What kind of e-mail account is it?

Click to expand...

I have 2 yahoo email accounts

miles01110 said:

"Yahoo" is not what I meant by "type of e-mail account," so I probably should have been more clear. Are they POP(3) or IMAP accounts?

Click to expand...

I've added the accounts through Settings/Mail, Contacts, Calendars/Account... and I have no idea what kind of accounts are: pop3 or imap...
But after reading a little on Google it seems that iPhone uses IMAP to download emails from Yahoo ...

http://www.mobilewhack.com/iphone-uses-imap-to-download-yahoo-mail/

And now I notice that from my Hotmail account if I delete emails they just keep coming back!
I even went on my account from my pc deleted all emails... But they redownload on my iPhone...
Hotmail is pop3 account...

What the heck?

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And I'm not the only one with this problem:

http://discussions.info.apple.com/thread.jspa?messageID=12777140