mx1.paypalcorp.com has no MX records.
Question and response
Question
dig mx1.paypalcorp.com. MX
Answer
The response has no answer records.
Authority
paypalcorp.com. 300 SOA ppdns.paypal.com. hostmaster.paypal.com. 1969046569 7200 600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0