_spf.shared-server.net has no MX records.
Question and response
Question
dig _spf.shared-server.net. MX
Answer
The response has no answer records.
Authority
shared-server.net. 1800 SOA ns.namedserver.net. root.namedserver.net. 2772106865 10800 1800 259200 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0