We have two Exchange 5.5 servers, both running Enterprise Edition, connected via an X400 connector. The servers are in different sites and are connected via a 512k WAN link. Server A is a NT Server 4 SP6a machine, Server B is a Windows 2000 SP4 machine. We experienced very slow mail traffic between the two MTA's. Line utilisation was ±50%, both machines had low utilisation of hardware resources (HDD's, NIC's, CPU's, memory). Mtacheck did not pick up any database corruption. Normal flow of mail was only restored when we tried using a site connector between the two servers as a final test. This led us to believe that the problem might be X400 corruption. (Creating a second X400 connector did not solve the problem)