f.ns.admin.sardinasystems.com has no SRV records.
Question and response
Question
dig f.ns.admin.sardinasystems.com. SRV
Answer
The response has no answer records.
Authority
admin.sardinasystems.com. 60 SOA a.ns.admin.sardinasystems.com. hostmaster.admin.sardinasystems.com. 1772110968 300 60 604800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0