plesk31.okhosting.com has no MX records.
Question and response
Question
dig plesk31.okhosting.com. MX
Answer
The response has no answer records.
Authority
okhosting.com. 60 SOA okhosting.com. soporte\@okhosting.com.okhosting.com. 0 60 60 60 60
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0