Internet mail for small network

We have recently connected our small (4 PCs) network to the internet using ADSL. Previously I used a dial-up connection to send and retrieve mail from one PC. We now have the option of using mail (Outlook at present) from any PC, unfortunately I can see no way of keeping track of sent or recieved mail as it could reside on any of the PCs on the network. We currently use only one domain e-mail account. Does anyone have any ideas ?