mail4.netdesignmail.com has no TXT records.
Question and response
Question
dig mail4.netdesignmail.com. TXT
Answer
The response has no answer records.
Authority
netdesignmail.com. 3600 SOA ns1. hostmaster. 22 900 600 86400 3600
Additional
. 0 OPT ; payload 4000, xrcode 0, version 0, flags 0