PPC WM5 and Exchange 2003 SP2 ActiveSync

I have a PPC (Dell Axim) with Windows Mobile 5 and a Exchange Server 2003
with SP2.

I just can access my e-mail by Internet with my PPC (by WiFi or GPRS) when I
open, sync and close my Outlook 2003 in my workstation.

If I don't open my Outlook 2003, the activesync PPC can't get my e-mails.

Example:
I have 10 new e-mails in my mailbox on Exchange Server.
If I use my PPC over Internet, after the activesync I don't have any new
messages in my PPC (the activesync process occurs with no erros).
Now, If I open my Outlook 2003 in my desktop (or access by OWA), and then
close it, in the next time that I try to use my PPC, I can get all 10
menssages.

When I solve this problem ?

Thanks.