[fetchmail]fetchmail keep and new mail

Hi!

I am running fetchmail at my Linux server.
I have configure 1 account for downloading email without delete it.

But I have some problem here. My fetchmail run as daemon for every 600sec.

Fetchmail will alawys download my same message each time. How can I configure 
my fetchmail such as download only new message and without delete it.

Below is my fetchmail setting

poll pop.time.net.my
        proto POP3
        user wismaleader
        pass 123456
        is wismaleader
        keep

Best regards,
WismaLeader