mail.bolt112a.mxthunder.net has no SRV records.
Question and response
Question
dig mail.bolt112a.mxthunder.net. SRV
Answer
The response has no answer records.
Authority
bolt112a.mxthunder.net. 86400 SOA ns.dnsbox.net. hostmaster.dnsbox.net. 2018120308 10000 3600 604800 172800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0