mx.z.com has no TXT records.
Question and response
Question
dig mx.z.com. TXT
Answer
The response has no answer records.
Authority
z.com. 1800 SOA ns1.cf.gmointernet.jp. dns.cloudflare.com. 2396445585 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0