ns4.aciglobal.com has no MX records.
Question and response
Question
dig ns4.aciglobal.com. MX
Answer
The response has no answer records.
Authority
aciglobal.com. 300 SOA ns1.aciglobal.com. hostmaster.aciglobal.com. 2026012901 10800 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0