ws00.flex1.net has no MX records.
Question and response
Question
dig ws00.flex1.net. MX
Answer
The response has no answer records.
Authority
flex1.net. 900 SOA ns1.flex1.net. noc.flex1.net. 110 900 300 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0