mx1.intercom.com.sv has no NS records.
NS records for this zone are defined at intercom.com.sv.
NS records for this zone are defined at intercom.com.sv.
Question and response
Question
dig mx1.intercom.com.sv. NS
Answer
The response has no answer records.
Authority
intercom.com.sv. 86400 SOA ns1.intercom.com.sv. hostmaster.intercom.com.sv. 20200809 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0