Robtex

Up: 204.51.160.0/20
Can't show all results, try to descend to a more specific CIDR
Down left: 204.51.160.0/22
Down right: 204.51.164.0/22

IP	Type	Hostname
204.51.165.10	PTR	mail2528.nationalgiftcards.com
204.51.165.11	PTR	mail2529.nationalgiftcards.com
204.51.165.18	PTR	mail2536.nationalgiftcards.com
204.51.165.32	PTR	mail2550.nationalgiftcards.com
204.51.165.33	PTR	mail2551.nationalgiftcards.com
204.51.165.72	PTR	mail2590.nationalgiftcards.com
204.51.165.112	PTR	mail2630.nationalgiftcards.com
204.51.165.128	PTR	mail2646.nationalgiftcards.com
204.51.165.153	PTR	mail2671.nationalgiftcards.com
204.51.165.160	PTR	mail2678.nationalgiftcards.com
204.51.165.176	PTR	mail2694.nationalgiftcards.com
204.51.165.210	PTR	mail2728.nationalgiftcards.com