So, my firewall has just w2k sp 2 and ISA server. It has 2 nic cards. I did not install the compute browser, fax service, licence logging, distributed file system and distributed link tracing services. On my external link card, I disabled the client for microsoft network, file and printing sharing, register this connection in DNS and netbios. Is it possible that the problem comes from the configuration of my Exchange server ? Thanks a lot Arnaud Forster