Robtex

Up: 216.247.40.0/21
Can't show all results, try to descend to a more specific CIDR
Down left: 216.247.44.0/23
Down right: 216.247.46.0/23
(Some of the IP numbers are capped at 3 entries)

IP	Type	Hostname
216.247.44.134	PTR	mail.thewalters.org
216.247.44.149	PTR	mail.supperclub.co.uk
216.247.44.236	PTR	mail.farsidic.com
216.247.44.236	PTR	mail.findiranian.com
216.247.44.236	PTR	mail.irnex.com
216.247.45.76	A	mail.3m-store.com
216.247.45.149	PTR	mail.t-funk.com
216.247.45.156	PTR	mail.notaboutus.com
216.247.45.176	PTR	mail.zyport.com
216.247.45.185	PTR	mail.sorsco.com
216.247.45.211	PTR	mail.tomcampbell.com
216.247.45.216	A	mail.loscalifornianos.net
216.247.46.1	PTR	mail.jhoe.com
216.247.46.1	PTR	int-5500.interland.net
216.247.46.55	PTR	mail.centaurcelluloid.com
216.247.46.107	PTR	mail.ilinx.com
216.247.46.152	PTR	mail.destek.com.tr
216.247.47.46	PTR	mail.musiciansboulevard.com
216.247.47.154	PTR	mail.sundeep.net
216.247.47.232	PTR	mail.hexnet.com
216.247.47.232	PTR	mail.theedgemag.com
216.247.47.233	PTR	mail.rxsites.com