Received: from mail-oi0-f49.google.com (209.85.218.49) by
$ host mail-oi0-f49.google.com
mail-oi0-f49.google.com has address 209.85.218.49
$ host -t PTR 209.85.218.49
49.218.85.209.in-addr.arpa domain name pointer mail-oi0-f49.google.com.
Received: from sender2.dc2.reg.ru (sender2.dc2.reg.ru. [31.31.204.234])
Ну и туда-же