mail2.isdn.net has one IP number , which also has a corresponding reverse pointer. tsg1.com, 1220.com, sbadv.com, tftco.net, saftek.com and at least 100 other hosts use this as a mailserver. isdn.net is a domain controlled by three nameservers at isdn.net themselves. All of them are on different IP networks. Incoming mail for isdn.net is handled by four mailservers. All of them are on the same IP network. isdn.net has one IP number. mail2.isdn.net is hosted on a server in United States.