mx-01.mail-forwarder.io has no TXT records.
Question and response
Question
dig mx-01.mail-forwarder.io. TXT
Answer
The response has no answer records.
Authority
mail-forwarder.io. 900 SOA ns-590.awsdns-09.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0