Mails sent from hmailserver marked as spam when domain is the one having the server's secondary ip

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http://serverfault.com – I have a Windows 2008 Server, hosting 2 different domains. Domain A is using the server's main IP, while domain B is using server's secondary ip. I have setup these 2 domains in hmailserver, and mails are sent successfully, but the ones sent from domain B are marked as spam by the most famous mail providers (hotmail, gmail etc). Mails from domain A are delivered normally (not spam). Do you have any idea on what is going wrong? (HowTos)