go
imap.gtz.de has one IP number , but the reverse is vm-isa2006-ep.gtz.de. owa.gtz.de, pop.gtz.de, owasmtp.gtz.de and vm-isa2006-ep.gtz.de point to the same IP. gtz.de is a domain controlled by two nameservers at ns.de.uu.net. They are on different IP networks. Incoming mail for gtz.de is handled by three mailservers at gtz.de themselves. All of them are on the same IP network. gtz.de has one IP number. imap.gtz.de is hosted on a server in Germany.

imap.gtz.de
a records
 
+ 193.97.170.153 193.97.168.0/21 AS28940 vm-isa2006-ep.gtz.de
+ --- vm-isa2006-ep.gtz.de

gtz.de
a records
 
+ 193.97.170.91 193.97.168.0/21 AS28940  
+ ---  
ns-soa records
 
+   AS?  
+ ---  
ns records
auth04.ns.de.uu.net
+ 192.76.144.17 192.76.144.0/24 AS12234 -
+ --- -
auth54.ns.de.uu.net
+ 194.128.171.100 194.128.0.0/14 AS702 -
mx records
smtp15.gtz.de
+ 193.97.170.15 193.97.168.0/21 AS28940 -
+ --- -
smtp4.gtz.de
+ 193.97.170.9 193.97.168.0/21 AS28940 -
smtp16.gtz.de
+ 193.97.170.16 193.97.168.0/21 AS28940 -
ip numbers of host
193.97.170.153
ptrs of ip numbers
vm-isa2006-ep.gtz.de
ip numbers using ptr to this host
193.97.170.117
193.97.170.77
hostnames sharing ip with a-records
owa.gtz.de
owasmtp.gtz.de
pop.gtz.de
vm-isa2006-ep.gtz.de