ns.ntt.ru has no MX records.
Question and response
Question
dig ns.ntt.ru. MX
Answer
The response has no answer records.
Authority
ntt.ru. 3600 SOA ns.ntt.ru. george.ntt.ru. 20091587 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0