outlook blocklist

The outlook blocklist tag covers discussions about Microsoft's email block lists that prevent legitimate messages from reaching Outlook.com and Microsoft 365 recipients. Recent threads describe widespread deliverability failures where senders receive 550 errors referencing block list codes like S3150, even when their mail passes authentication checks. Affected users include small businesses, ISPs, and healthcare services that find their emails bounced or rate-limited without clear cause. Topics include troubleshooting block list removals, understanding Microsoft's filtering criteria, and navigating support responses that often claim no issue exists. The tag is relevant for IT administrators and email senders dealing with Outlook deliverability problems.