_netblocks.synchronoss.com has no MX records.
Question and response
Question
dig _netblocks.synchronoss.com. MX
Answer
The response has no answer records.
Authority
synchronoss.com. 900 SOA ns1.synchronoss.com. networkengineers.synchronoss.com. 812 10800 3600 604800 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0