Windows error 8380 (ERROR_DS_DUP_MAPI_ID): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: A schema attribute reuses a MAPI identifier already assigned to another definition.

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ERROR_DS_DUP_OID	ERROR_DS_DUP_SCHEMA_ID_GUID

ERROR_DS_DUP_MAPI_ID

The mAPIID value collides with an existing attributeSchema object

The optional mAPIID field associates an Active Directory attribute with a MAPI property identifier. MS-ADTS includes this value in the uniqueness checks for attributeSchema updates. A duplicate means another schema attribute already owns the same identifier, so the proposed definition cannot be accepted as written.

Treat this separately from duplicate OID or duplicate LDAP display name errors. Search the schema NC by mAPIID and identify the existing attribute. Mail-related schema extensions and legacy integrations may carry historical assignments, so blindly choosing another numeric value can break interoperability. The schema package owner should provide the correct non-conflicting identifier or remove the optional mapping when it is not required.

What to inspect

Query the schema NC for the proposed mAPIID value.
Compare the colliding attribute with the schema package and product version being installed.
Do not renumber a published MAPI mapping without understanding the consuming application.

References

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