ns4.nicusa.com has no MX records.
Question and response
Question
dig ns4.nicusa.com. MX
Answer
The response has no answer records.
Authority
nicusa.com. 1800 SOA glns-1.cdc.nicusa.com. dnsadministrator.egov.com. 2025040801 86400 3600 3600000 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0