Timeout error at remote location

We have recently moved our mail services out of house and our users in a remote location on our WAN, but without a domain controller(PDC or BDC) are experiencing timeout errors with Outlook 2000. I’ve set the timeout to 5 minutes but they can only send, not recieve. I’ve double checked the settings but have found no problems. Another remote location does not have this problem. If anyone needs more info to solve this please don’t hesitate to e-mail me. Thanks!