An Internet-based Document Delivery Service (DDS) has been developed within the framework of the CNR ( the Italian Research National Council) Project BiblioMIME, in order to take advantage of new Internet technologies and promote cooperation among CNR and Italian university libraries. Adopting such technologies changes the traditional organisation of DDS and may drastically reduce costs and delivery times. An information system managing DDS requests and monitoring the temporal evolution of the service has been implemented, running on the local-area network of a test-site library. It aims to track number and types of documents requested and received, user distribution, delivery times and types (surface mail, fax, Internet), to automate repetitive manual procedures and to deal with the various accounting methods used by other libraries. Transmission of documents is carried out by means of an e-mail/Web gateway system supporting document exchange via Internet, which assists receiving libraries in retrieving requested documents. This paper describes the architecture and main design features of the e-mail/Web gateway server (the BiblioMime server). This approach permits librarians to continue using e-mail service to send large documents, while resolving problems that users may encounter when downloading large size files with e-mail agents. The library operator sends the document as an attachment to the destination address; on fly the e-mail server extracts and saves the attachments in a web-server disk file and substitutes them with a new message part that includes an URL pointing to the saved document. The receiver can download these large objects by means of a user-friendly browser. We further discuss the data gathered during the triennium 1998-2000; this consists of about 5,000 DDS transactions per annum with 300 other Italian scientific and bio-medical libraries and commercial document suppliers. Use of the instruments described above allowed us to evaluate the performance of service "before" and "after" the use of Internet Document Delivery and to extract some critical data regarding DDS. Those include: a) libraries with which we have greater numbers of exchanges and their turnaround times; b) extraordinary reduction in costs and delivery times; c) the most frequently requested serial titles (allowing cost-effective decisions on new subscriptions); d) impact on DDS of library participation in consortia which allow user access to greater numbers of online serials.