We are currently experiencing a problem where by when messages are sent to our office, a delivery status notification failure message is being sent back to the sender, but the messages are being received. This only happens with three addresses that are hosted by our ISP, and then forwarded to us. They have assuredus the problem is not at their end by I am not sure. I have checked our spam filter program surf control, and this does not seem to be causing the problem, as if the messages are held by surfcontrol the error message is not sent until it is released. We are using Windows 2000 server for our domain, and Windows 2000 exchange server. Any help would be most appreciated. Thanks Danny