mail.explora.com.sv has no CNAME records.
Question and response
Question
dig mail.explora.com.sv. NS
Answer
The response has no answer records.
Authority
explora.com.sv. 5864 SOA gcasrv.explora.com.sv. bjaime\@explora.com.sv. 2026021100 10801 3600 1209600 38400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0