ns1.isi.com.do has no MX records.
Question and response
Question
dig ns1.isi.com.do. MX
Answer
The response has no answer records.
Authority
isi.com.do. 1800 SOA ns2.no-ip.com. hostmaster.no-ip.com. 2022064703 10800 1800 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0