mail.cas.dk has one IP number. dtl.dk, tto.se, tto.dk, bsds.dk, fangel.dk and at least 61 other hosts point to the same IP. cas.dk is a domain controlled by five nameservers at gratisdns.dk. All of them are on different IP networks. Incoming mail for cas.dk is handled by one mailserver at cas.dk themselves. cas.dk has one IP number. mail.cas.dk is hosted on a server in Denmark.