It won't be a Virgin fault. The relationship is between your iinet account with your iphone mobile. I would hazard a guess it's the mail settings.
Have you followed the instructions on the iinet website step by step?
Eg, make sure you enable SSL, the ports are correct for POP/IMAP
Read this part of the link I've given you:
"Email servers for other providers
If you have an iiNet Group mailbox, but your internet connection is with a non-iiNet Group provider, you’ll need to set the incoming mail server as listed above in order to receive email. To send emails, you’ll need to either:
A) Recommended: Set your iiNet Group outgoing mail server (listed above) with port 587 and ensure that outgoing authentication is enabled, using the username and password for your iiNet Group email account. This is a more 'permanent' solution that should prevent you needing to adjust your settings if you have multiple internet service providers. Alternatively, simply log in to webmail."
I'm not sure your exact circumstance, but the port is different to the one you've tried. Make sure you read iinet's instructions clearly.