mail.isol.cz has one IP number , which is the same as for isol.cz. mail.isol.cz also has a corresponding reverse pointer. sph.cz, in1.cz, ord.cz, xt3.cz, isol.cz and at least 100 other hosts point to the same IP. in1.cz, ord.cz, xt3.cz, a-ha.cz, sota.cz and at least 100 other hosts use this as a mailserver. isol.cz is a domain controlled by two nameservers at isol.cz themselves. They are on the same IP network. Incoming mail for isol.cz is handled by one mailserver also at isol.cz. mail.isol.cz is hosted on a server in Czech Republic.