mail.firstdatacorp.com has no CNAME records.
Question and response
Question
dig mail.firstdatacorp.com. NS
Answer
The response has no answer records.
Authority
firstdatacorp.com. 268 SOA dns2.p07.nsone.net. domainadmin.firstdata.com. 590215770 1200 180 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0