mx1.b26.cz has one IP number , which also has a corresponding reverse pointer. smtp.b26.cz and mx1.guarant.cz point to the same IP. cg.cz, ys.cz, cet.cz, gcf.cz, gme.cz and at least 100 other hosts use this as a mailserver. b26.cz is a domain controlled by two nameservers at broadnet.cz. They are on the same IP network. Incoming mail for b26.cz is handled by three mailservers at b26.cz themselves. All of them are on the same IP network. mx1.b26.cz is hosted on a server in Czech Republic.