Summary
mx0.gmx.net has one IP number , which also has a corresponding reverse pointer.
mx0.gmx.de point to the same IP.
gmx.at,
gmx.de,
gmx.ch,
hvdb.de,
gmx.net and at least 100 other hosts use this as a mailserver.
gmx.net is a domain controlled by two nameservers on different IP networks. Incoming mail for
gmx.net is handled by two mailservers at
gmx.net themselves. They are on the same IP network.
gmx.net has one IP number.
mx0.gmx.net is hosted on a server in Germany.