Prior to GDR2 update for Windows Phone, Gmail push used to work, which means email messages used to be downloaded the instant they got into inbox. After GDR2 update, Gmail checking frequency was set to 30 minutes. This was done as Google will be stopping ActiveSync services for new Gmail accounts in December 2013. To enable push again, follow these directions.
Goto settings -> Emails + accounts
add an account
enter email and password
set server as ‘m.google.com’
click next and push is enabled.
My old account was already m.google.com, and I just had to change interval from 30 minutes to when new mail arrives.
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