adns4.upenn.edu has no MX records.
Question and response
Question
dig adns4.upenn.edu. MX
Answer
The response has no answer records.
Authority
upenn.edu. 600 SOA ipam2.nnn.upenn.edu. hostmaster.upenn.edu. 2002368300 10800 3600 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0