Outlook 2010 not receiving emails

[#1]

I am helping a friend who has his domain registered with PlusNet. When I set up Outlook 2010 it runs the connection test and reports success. The test message, however, remains on the PlusNet mail server and is not uploaded to the local machine. He can send emails from Outlook OK but any incoming ones stay on the PN server and can be read OK using webmail.  Does anyone have any idea what is going on here?  Thanks for reading this.

[#2]

Make sure you tick the option to delete messages off server after downloading.
My dad didn't and he's just gone through 3000 messages on his iPad which re-downloaded 

[#3]

*edit - only do this once you've got them coming into your Outlook without a problem.