ns2.rainbowtel.net has no MX records.
Question and response
Question
dig ns2.rainbowtel.net. MX
Answer
The response has no answer records.
Authority
rainbowtel.net. 300 SOA ns1.rainbowtel.net. chrism.rainbowtel.com. 2025090377 10800 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0