reply.s50.exacttarget.com has no CNAME records.
Question and response
Question
dig reply.s50.exacttarget.com. NS
Answer
The response has no answer records.
Authority
s50.exacttarget.com. 158 SOA dns1.p01.nsone.net. hostmaster.nsone.net. 1680024972 7200 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0