Incoming mail for cm.sonera.com is handled by one mailserver at cm.sonera.com themselves. nmg.fi, smr.fi, ccc.fi, ntm.fi, rpc.fi and at least 100 other hosts share mailservers with this domain. mail.cm.sonera.com are subdomains to this hostname. sonera.com is a domain controlled by four nameservers. All of them are on different IP networks. Incoming mail for sonera.com is handled by two mailservers on different IP networks.