www.ccd.uns.ac.rs has no MX records.
Question and response
Question
dig static.169.145.243.136.clients.your-server.de. MX
Answer
The response has no answer records.
Authority
243.136.clients.your-server.de. 86400 SOA ns1.your-server.de. postmaster.your-server.de. 2012121800 86400 1800 3600000 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0