prfXXX.tmp folders in Netscape 7

[mkirros]

One of our computer users has had folders showing up in his Netscape 7 e-mail account which he did not create. The folders are named prfXXX.tmp (where XXX is any alphanumeric character) and they contain old e-mails which he has previously deleted. When he deletes the folders, they reappear the next time he starts Netscape. The computer is running WinXP on a network with a Win2K Server as PDC. Manually deleting the folders from the hard drive on the server has not worked either. The folders have now become so large that they are interfering with the functioning of his e-mail. Does anybody have any ideas on what these are and how to get rid of them? Thanks.