postoffice.hostrocket.com has no SRV records.
Question and response
Question
dig postoffice.hostrocket.com. SRV
Answer
The response has no answer records.
Authority
hostrocket.com. 1800 SOA elinore.ns.cloudflare.com. dns.cloudflare.com. 2392798026 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0