Jeroen, A quick check of those IPs shows that most don't have rDNS records. Make sure the A and PTR records for the mail server match the hostname it is using in the outbound SMTP session. Hope that helps, Adam Stasiniewicz ________________________________ From: owner-nanog@merit.edu on behalf of Jeroen Wunnink Sent: Wed 4/25/2007 1:22 PM To: nanog@merit.edu Subject: Hotmail blackholing certain IP ranges ? Does anyone have a clue why hotmail is appearantly blocking certain IP ranges ? I provided a new server for a customer in his own IP subnet which is a part of a /20 we announce, but for some reason all mail sent to @hotmail.com addresses disappears. He has another server in a /24 we announce which is still part of another network and that works like a charm. None of our subnets are blacklisted in any spamfilter I can find, so i'm a bit puzzeled on what's up here. If any hotmail netadmin is reading this list, can you please check if 81.26.212.0/26 is blocked in any way (It's part of 81.26.208.0/20 originating from AS39556) According to the mailserver logs all the mail is properly accepted by the hotmail relays, never to be seen again after that. Met vriendelijke groet, Jeroen Wunnink, EasyHosting B.V. Systeembeheerder systeembeheer@easyhosting.nl telefoon:+31 (035) 6285455 Postbus 48 fax: +31 (035) 6838242 3755 ZG Eemnes http://www.easyhosting.nl <http://www.easyhosting.nl/> http://www.easycolocate.nl <http://www.easycolocate.nl/>