res.spectrum.com has no MX records.
Question and response
Question
dig res.spectrum.com. MX
Answer
The response has no answer records.
Authority
res.spectrum.com. 14400 SOA auth1.charter.com. hostmaster.charter.com. 2019211617 7200 3600 604800 14400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0