ns03.ns.sip.is has no MX records.
Question and response
Question
dig ns03.ns.sip.is. MX
Answer
The response has no answer records.
Authority
sip.is. 2560 SOA ns01.ns.sip.is. hostmaster.sip.is. 1772546165 16384 2048 1048576 2560
Additional
The response has no additional records.