de.timeserver.pub has no MX records.
Question and response
Question
dig de.timeserver.pub. MX
Answer
The response has no answer records.
Authority
timeserver.pub. 3600 SOA hydrogen.ns.hetzner.com. dns.hetzner.com. 2026011600 86400 10800 3600000 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0