The SPNSuffixes element contains the SPN suffixes for the forest.

 <xs:element name="SPNSuffixes" nillable="true" type="sera:ArrayOfstring" />

The SPNSuffixes element is populated from the crossRefContainer!msDS-SPNSuffixes multivalued attribute on the Partitions Container object ([MS-ADTS] section If the crossRefContainer!msDS-SPNSuffixes attribute is not present or cannot be read due to the client lacking access rights to read the attribute, the server returns a null ActiveDirectoryForest/UPNSuffixes element.