mail.runbox.com has no TXT records.
Question and response
Question
dig mail.runbox.com. TXT
Answer
The response has no answer records.
Authority
runbox.com. 3600 SOA dns61.copyleft.no. hostmaster.copyleft.no. 3000010759 14400 3600 1296000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0