The Exchange 5.5 migration process uses X500 addresses in two different ways:
Ensure that the connection agreement includes X500 addresses with replicated objects. The inter-organizational Active Directory Connector (ADC) is used to replicate the Exchange 5.5 directory information to Active Directory, and to stamp replicated objects with the X500 address of the Exchange 5.5 mailbox. This feature is available only with Exchange 2000 Service Pack 1 (SP1). If you used the inter-organizational ADC before installing Exchange 2000 SP1, you must install Exchange 2000 SP1 and replicate again.
Important By default, ADC does not include X500 addresses with user objects. Use either LDP or ADSI Edit to assign the value SMTP,X500 to the msExchInterOrgAddressType attribute on the connection agreement object in Active Directory. LDP and ADSI Edit are available on the Windows 2000 Server compact disc in the \Support\Tools folder.