o7.domain.flock.co has no MX records.
Question and response
Question
dig o7.domain.flock.co. MX
Answer
The response has no answer records.
Authority
flock.co. 900 SOA ns-176.awsdns-22.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0