The AllowedDNSSuffixes element contains an array of DNS suffixes for this domain.

      name="AllowedDNSSuffixes" nillable="true" type="sera:ArrayOfstring" />

The AllowedDNSSuffixes element is populated from the domainDNS!msDS-AllowedDNSSuffixes multivalued attribute on the domain NC root object ([MS-ADTS] section If the domainDNS!msDS-AllowedDNSSuffixes attribute is not present or cannot be read due to the client lacking access rights to read the attribute, the server returns a null ActiveDirectoryDomain/AllowedDNSSuffixes element.