ns3.northwestern.edu has no MX records.
Question and response
Question
dig ns3.northwestern.edu. MX
Answer
The response has no answer records.
Authority
northwestern.edu. 600 SOA infoblox.ittns.northwestern.edu. hostmaster.northwestern.edu. 4026732508 14400 3600 604800 600
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0