rmail4.eresources.com has no MX records.
Question and response
Question
dig rmail4.eresources.com. MX
Answer
The response has no answer records.
Authority
eresources.com. 180 SOA ns11.constellix.com. dns.constellix.com. 2015010687 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0