mailgw.ibw.com has no CNAME records.
Question and response
Question
dig mailgw.ibw.com. NS
Answer
The response has no answer records.
Authority
ibw.com. 2111 SOA ns1.intercom.com.sv. hostmaster.intercom.com.sv. 20210793 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0