ntp.ntstime.org has no MX records.
Question and response
Question
dig ntp.ntstime.org. MX
Answer
The response has no answer records.
Authority
ntstime.org. 86400 SOA root-dns.netcup.net. dnsadmin.netcup.net. 2024102203 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0