Manual Schema Changes Are Lost When You Apply Exchange Server 2003 Schema over Exchange 2000 Server Schema

When you apply the Exchange Server 2003 schema over an existing Microsoft Exchange 2000 Server schema, any manual changes that were made previously to the Exchange 2000 schema are lost.

Exchange Server 2003 Setup updates the Microsoft Active Directory directory service schema and overwrites the existing Exchange 2000 schema information.

In an Exchange 2000 environment that has only Exchange 2000 schema extensions applied, the ms-Exch-Schema-Version-Pt attribute has a rangeUpper value set to 4397. Microsoft Exchange 2000 Server Setup uses this value to determine if any schema updates are necessary when you run the setup /forestprep command. If setup /forestprep is run again, Setup sees that the value of ms-Exch- Schema-Version-Pt is still set to 4397. Setup does not make any additional schema updates. As a result, any manual modifications to the schema are preserved.

Exchange Server 2003 reads the same attribute, but if it detects that the value is set to 4397 or to any value that is lower than the Exchange Server 2003 schema version, it extends the schema by importing files Schema0.ldf through Schema9.ldf. Previous manual updates are changed in favor of the new schema.

To work around this behavior, you must reapply the manual changes after Exchange Server 2003 has updated the schema.

This is typical behavior for Exchange 2000 and Exchange Server 2003 when you run Setup.