Microsoft Outlook-2007

hi all,

I am having one computer where every mail which are going out from my company ( eg. 50 user )are downloading in this computer, My user is facing a problem while mails are downloading, he is unable to do anything one that computer,
as i know in outlook-2003 & 2007 .pst file size is by default is 20 GB but this computer can only store upto 8 GB. then i have to create new pst or to delete some mails from it. i have set up manual send & receive but it is not at all working, still it start downloading any time that is the big problem.

can anybody give me the proper solution for that.