sslvpn.staff.onr.com has no MX records.
Question and response
Question
dig sslvpn.staff.onr.com. MX
Answer
The response has no answer records.
Authority
onr.com. 14400 SOA ns1.onr.com. domains.onr.com. 2022040501 10800 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0