mx-gw.ispmail.de has one IP number , which also has a corresponding reverse pointer. mail.probizz.ch and mail.berufsgeheimnistraeger.de point to the same IP. ssl.de, trv.de, jop.net, etd.net, wuth.com and at least 100 other hosts use this as a mailserver. ispmail.de is a domain controlled by three nameservers at ispmail.de themselves. Two nameservers have the same IP number. They are on the same IP network. Incoming mail for ispmail.de is handled by two mailservers also at ispmail.de. They are on different IP networks. ispmail.de has one IP number. mx-gw.ispmail.de is hosted on a server in Switzerland even though the hostname implies Germany.