spf-gates.sureserver.com has no MX records.
Question and response
Question
dig spf-gates.sureserver.com. MX
Answer
The response has no answer records.
Authority
sureserver.com. 2560 SOA sgate1.sureserver.com. hostmaster.sureserver.com. 1772123615 16384 2048 1048576 2560
Additional
The response has no additional records.