aztestsmtp.brassring.com has no MX records.
Question and response
Question
dig aztestsmtp.brassring.com. MX
Answer
The response has no answer records.
Authority
brassring.com. 3600 SOA a1-160.akam.net. hostmaster.hiresystems.com. 2015092183 10800 600 86400 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0