sysmail1.linecorp.com has no TXT records.
Question and response
Question
dig sysmail1.linecorp.com. TXT
Answer
The response has no answer records.
Authority
linecorp.com. 600 SOA ns2.naver.jp. domain.linecorp.com. 1772089968 3538 600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0