ptns.pearson.com has no MX records.
Question and response
Question
dig ptns.pearson.com. MX
Answer
The response has no answer records.
Authority
ptns.pearson.com. 900 SOA dns-apac-1.ptns.pearson.com. gns-dnsoperations.pearson.com. 1093 900 900 2592000 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0