vpn.longlines.com has no MX records.
Question and response
Question
dig vpn.longlines.com. MX
Answer
The response has no answer records.
Authority
longlines.com. 3600 SOA ns1.longlines.com. postmaster.longlines.com. 721599979 7200 3600 1728000 14400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0