Been there, done that. And then Microsoft answers my complaints (after my mails never showed up at my brother in laws outlook.com mailbox): We have reviewed yo

Been there, done that. And then Microsoft answers my complaints (after my mails never showed up at my brother in laws outlook.com mailbox): We have reviewed your IP(...) and determined that messages are being filtered based on the recommendations of the SmartScreen® Filter. Email filtering is based on many factors, but primarily it's due to mail content and recipient interaction with that mail. Because of the proprietary nature of SmartScreen® and because SmartScreen® Filter technology is always adapting and learning more about what is and isn't unwanted mail, it is not possible for us to offer specific advice about improving your mail content. However, in general SmartScreen® Filter evaluates specific words or characteristics from each e-mail message and weights them, based on their likelihood to indicate that a message is unwanted or legitimate mail. Unfortunately, after reviewing the information you provided and in compliance with our mail policies, we are unable to offer immediate mitigation for your deliverability issue. However, we have some specific recommendations for you to consider that can help you to improve deliverability over time. It's a struggle running your own mailserver.