vpn.sip.com.tr has no MX records.
Question and response
Question
dig vpn.sip.com.tr. MX
Answer
The response has no answer records.
Authority
sip.com.tr. 1800 SOA clayton.ns.cloudflare.com. dns.cloudflare.com. 2396970007 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0