filter20.antispamcloud.com has no NS records.
NS records for this zone are defined at antispamcloud.com.
NS records for this zone are defined at antispamcloud.com.
Question and response
Question
dig filter20.antispamcloud.com. NS
Answer
The response has no answer records.
Authority
antispamcloud.com. 900 SOA ns-781.awsdns-33.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0