ams.wordpress.com has no MX records.
Question and response
Question
dig ams.wordpress.com. MX
Answer
The response has no answer records.
Authority
ams.wordpress.com. 300 SOA ns1.wordpress.com. hostmaster.wordpress.com. 2005071863 14400 7200 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0