mx1.mail.level3.net has no TXT records.
Question and response
Question
dig mx1.mail.level3.net. TXT
Answer
The response has no answer records.
Authority
Level3.net. 3600 SOA ns2.Level3.net. dns.level3.net. 2026022400 7200 600 2592000 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0