Robtex

Up: 216.163.176.0/20
Can't show all results, try to descend to a more specific CIDR
Down left: 216.163.184.0/22
Down right: 216.163.188.0/22
(Some of the IP numbers are capped at 3 entries)

IP	Type	Hostname
216.163.188.4	PTR	c9bigip.prontomail.com
216.163.188.10	PTR	c9mailgw.prontomail.com
216.163.188.32	A	server.f-prot.com
216.163.188.32	A	fprot5.ctmail.com
216.163.188.32	A	avdl.5.geo.ctmail.com
216.163.188.34	PTR	c9ipres.ctmail.com
216.163.188.36	PTR	commtouch.com
216.163.188.40	A	blogs.authentium.com
216.163.188.43	PTR	asmtp.ctmail.com
216.163.188.43	PTR	c9asmtp.ctmail.com
216.163.188.43	PTR	pop.ctmail.com
216.163.188.45	PTR	c9resolver.ctmail.com
216.163.188.45	A	resolver3.ast.ctmail.com
216.163.188.45	A	resolver5.icew.ctmail.com
216.163.188.48	A	server.f-prot.com
216.163.188.48	A	directupdates.f-prot.net
216.163.188.49	A	webres2.netasq.ctmail.com
216.163.188.49	A	webres5.incr.ctmail.com
216.163.188.53	PTR	c9bh.prontomail.net
216.163.188.56	PTR	commtouch.com
216.163.188.56	PTR	commtouch.info
216.163.188.56	A	cpsserv.org
216.163.188.58	PTR	eforwardct.name-services.com
216.163.188.60	PTR	mx01.mx-server.net
216.163.188.64	A+PTR	c9mailgw.ctmail.com
216.163.188.74	A	dtcwsd.1.geo.ctmail.com
216.163.188.75	A	ctasd2.dtek.ctmail.com
216.163.188.75	A	c1ctasd1.ctmail.com
216.163.188.76	PTR	wn.cpsserv.com
216.163.188.76	A	wn.1.geo.ctmail.com
216.163.188.82	A	auth.1.geo.ctmail.com
216.163.188.83	A	cyren.co.il
216.163.188.83	A	cyyren.com
216.163.188.83	A	cyrenn.com
216.163.188.96	A	olympus.1.geo.ctmail.com
216.163.188.100	A	fwd1.emm.ctmail.com
216.163.188.100	A	mxclean.maslaton.com
216.163.188.147	A	login8.cpsserv.com
216.163.188.153	A+PTR	ns1.ctmail.com
216.163.188.153	A	httpdns.1.geo.ctmail.com
216.163.188.154	PTR	c9intdns.prontomail.com
216.163.188.154	A	ns99.ctmail.com
216.163.188.156	A	ns1.amadis.com
216.163.188.198	A	server.f-prot.com
216.163.188.200	A+PTR	c9outbound200.ctmail.com
216.163.188.201	A+PTR	c9outbound201.ctmail.com
216.163.188.202	A+PTR	c9outbound202.ctmail.com
216.163.188.203	A+PTR	c9outbound203.ctmail.com
216.163.188.208	A+PTR	c9outbound208.ctmail.com
216.163.188.209	A+PTR	c9outbound209.ctmail.com
216.163.188.210	A+PTR	c9outbound210.ctmail.com
216.163.188.220	PTR	c9outbound220.ctmail.com
216.163.188.221	PTR	c9outbound221.ctmail.com
216.163.188.230	A	c9outbound230.ctmail.com
216.163.188.254	A+PTR	ftp.ctmail.com
216.163.191.2	PTR	corp.commtouch.com
216.163.191.3	PTR	corp.commtouch.com