iPhone Email Pop - Up notifications

[iPNewb]

Just got my iPhone 3G on 3.1.3 (dreading iOs4 update).

I'm confused about email pop-up notifications.
I have jailbroken & unlocked the phone everything seems to running fine
except I get no pop up notifications like I do for sms, I hear a sound & that's it.

I used Google's sync's instructions via Exchange, everything went through got my contacts set up. (I am using iPhone's native mail programme)

I've got all notifications turned on.

How do I get email pop-ups?

Thanks in advance.