RPC over HTTP on two different computers

Hi,
we have a user having a PC and a laptop. Both have Outlook 2003 and are configured on the Exchange server through HTTP over RPC. When she sends a mail on the laptop, it does not appear in the sent items of the PC and vice versa. We have made a test and sent a mail from the laptop to the PC but there too, the mail is not received on the PC. The persons to whom she sends the mail do not receive it too from the laptop.

Could you please advise.
Thanking you in advance for your response.