ca.frontiernet.net has no MX records.
Question and response
Question
dig ca.frontiernet.net. MX
Answer
The response has no answer records.
Authority
ca.frontiernet.net. 21600 SOA auth.roch.ny.frontiernet.net. hostmaster.frontiernet.net. 2602200019 10800 3600 604800 21600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0