Problem: Couldn't send email b/w exchange 2000 and 5.5 Returned mail from administrative ??? X.400 not present under the 5.5 Exchange Administrator under the Exchange 2000 computer or the ADC computer. The MTA was present in the computer running 5.5 but no MTA or X.400 in 2k server. Solution: From DC with ADC, went into AD Connector Manager, choose the connector with the DC's name, went into: Config CA_AdmGrp_DCName->Properties, schedule and checked the box "replicate the entire dir.." applied settings and right clicked CA_AdmGrp_DCName and choose replicate now. The X.400 connector then appeared in the 5.5 Exchange Administrator after restarting the application, under both Exchange 2000 computer and ADC Domain Controller.