_netblocks.northwestern.edu has no MX records.
Question and response
Question
dig _netblocks.northwestern.edu. MX
Answer
The response has no answer records.
Authority
northwestern.edu. 600 SOA infoblox.ittns.northwestern.edu. hostmaster.northwestern.edu. 4026692250 14400 3600 604800 600
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0