Even with a good IP reputation, specific content triggers can block an email. Microsoft's "SmartScreen" technology scans for:
Managing blocked emails in Hotmail (now part of Microsoft Outlook) involves two distinct scenarios: users wanting to block unwanted senders and users finding their own emails or accounts blocked by Microsoft's security systems. Managing Your Block List blocked emails hotmail
Microsoft does not use a single “block list.” Instead, it uses a multi-layered defense system: Even with a good IP reputation, specific content