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Yup, had this problem too. Just go into the mail settings on your iphone and reenter your password. It should fix it.
 
I'm having this problem now. What fixed it for you?

I changed my Gmail account password on the laptop, changed it in the Mail settings on the iphone and then tried to retrieve my mails, but a message pops up "...Password not recognized."
 
I deleted my Google account. I was having to do this sometimes twice a week due to "suspicious activity" and got damned tired of it. Imagine changing Google email and calendar passwords on an iPhone, a Macbook, and a Windows 7 laptop several times per week.

I don't even use Google as my home page anymore.
 
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