mx1.uberspace.is has no MX records.
Question and response
Question
dig mx1.uberspace.is. MX
Answer
The response has no answer records.
Authority
uberspace.is. 2560 SOA ns3.jonaspasche.com. hostmaster.uberspace.is. 1771243981 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0