What's the difference between "Exchange Legacy Distinguished Name" and "Active Directory Distingushed Name"?

Question

I'm a little confused by these two terms: "Legacy Distinguished Name"(Legacy DN) and "Distingushed Name"(DN).

The first term Legacy DN seems only for Exchange, while the latter DN is only mentioned for Active Directory.

They are obviously not in same format:

DN is like: CN=Morgan Cheng, OU= SomeOrg, DC=SomeCom, DC=com

LegacyDN is like: /o=SomeDomain/ou=SomeGroup/cn=Recipients/cn=Morgan Cheng

I am still not clear what exactly the differce is. Are they two totally differnt stuff? or just same info represented in two different forms?

And, why is it called "Legacy"? If it is legacy, something must be new, right?

Hope some AD and Exchang experts can give me some inputs.

Answer 1

In Exchange 5.5, Exchange was assigning distinguished names to accounts and mailboxes (Obj-Dist-Name). When Active Directory came along, Exchange 2000 and later would use its distinguished names instead. In order to preserve backwards compatibility, migration from Exchange 5.5 to Exchange 2000 carried over the old DNs into the legacyExchangeDN attribute of ActiveDirectory.

Some applications continue to refer to Obj-Dist-Name. To preserve compatibility with these applications, later exchange versions synthesize a legacyExchangeDN value even for objects that have not been migrated from Exchange 5.5. The RUS automatically sets it to some value, apparently to the same value as the distinguishedName in your case.

The "new" way (since 2000) is to refer to objects by distinguished name, not Obj-Dist-Name.