Hi allAfter I created a child domain, I found that my parent domain's DC/EX is unable to contact the child domain's DC/EX. For example, in Active Directory Users and Computers, I right click then select "Connect to Domain" and type in "child.parent.com", it returned "The domain child.parent.com could not be found because: The specified domain either does not exists or could not be contacted". Same as the EXs, parent EX is unable to forward message to the child EX. Messages are queued in the server queue.I tried the other way around, child domain's DC/EX can connect/manage the parent domain's DC/EX with no problem....I tried this KB: http://support.microsoft.com/kb/313167 but still no luck.Any suggestion is appreciated.Thank youCelic

Have you checked DNS? DNS is very important and often underestimated in a MS environment.