dfw.wordpress.com has no MX records.
Question and response
Question
dig dfw.wordpress.com. MX
Answer
The response has no answer records.
Authority
dfw.wordpress.com. 60 SOA ns1.wordpress.com. mmmmmm.gmail.com. 2005071973 14400 7200 604800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0