How to turn off email auto forward?

I have a 3G iphone and it's set up to retrieve email from my gmail account. I don't know how, but it has started trying to auto-forward my email to another account (my work blackberry). The emails don't go through so I keep getting a failure to send message for each email I have been receiving. I looked in settings and I don't see anything set up to forward email, I'm not sure how it started in the first place. How can I turn off the auto-forwarding?