Bigpond won't receive emails. (Mac mail on MacBook) What should iMap prefix be?

Should iMap prefix be blank? Our account was blocked because of an attempted scam. Telephone support with Telstra re-instated it, and set new password. It accepts password. I notice iMap prefix is blank. What should it be? We havn't had any incoming mail on bigpond since - we are getting it our other devices.