mail2.mailer.twinfield.com has no SRV records.
Question and response
Question
dig mail2.mailer.twinfield.com. SRV
Answer
The response has no answer records.
Authority
twinfield.com. 1800 SOA jihoon.ns.cloudflare.com. dns.cloudflare.com. 2398419897 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0