spf-proofpoint.isc.upenn.edu has no MX records.
Question and response
Question
dig spf-proofpoint.isc.upenn.edu. MX
Answer
The response has no answer records.
Authority
upenn.edu. 600 SOA ipam1.nnn.upenn.edu. hostmaster.upenn.edu. 2002363167 10800 3600 604800 600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0