harbor.ecn.purdue.edu has no MX records.
Question and response
Question
dig harbor.ecn.purdue.edu. MX
Answer
The response has no answer records.
Authority
ecn.purdue.edu. 86400 SOA harbor.ecn.purdue.edu. hostmaster.ecn.purdue.edu. 2388939731 10800 3600 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0