smtp.interdomain.org has no TXT records.
Question and response
Question
dig smtp.interdomain.org. TXT
Answer
The response has no answer records.
Authority
interdomain.org. 300 SOA ns1.interdomain.net. admin.interdomain.net. 467112996 28800 7200 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0