When I send an email to a Hotmail account, it is successfully sent out from the VPS. There is no delivery failure, no bounce, no other errors. The VPS IP is not on any spam block list. There is reverse DNS and SPF record. The Hotmail account is working as it receives mails from other domains on other servers. However, the email does not end up in Hotmail Inbox or Junk folder. It just disappears, apparently dropped on the Hotmail side, probably due to their filtering. If you first send a message from Hotmail to the VPS, then reply to that message, the reply arrives at Hotmail. I have submitted a ticket and support has looked into it. They say it is possible Hotmail has blocked my IP as the logs indicate there were some other failures sending/receiving to/from Hotmail. They confirm the logs indicate the message is delivered to Hotmail and can't say what happens on the Hotmail side. I am not sure if Hotmail will be helpful on this. I am wondering if anyone else is facing the same problem or has a solution. Or has contacted Hotmail about this and has more info.