a.spamfilter.steadfast.net has no SRV records.
Question and response
Question
dig a.spamfilter.steadfast.net. SRV
Answer
The response has no answer records.
Authority
steadfast.net. 1800 SOA asa.ns.cloudflare.com. dns.cloudflare.com. 2396006312 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0