adns2.nnn.upenn.edu has no MX records.
Question and response
Question
dig adns2.nnn.upenn.edu. MX
Answer
The response has no answer records.
Authority
upenn.edu. 600 SOA ipam1.nnn.upenn.edu. hostmaster.upenn.edu. 2002380470 10800 3600 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0