How does Microsoft SNDS relate to blocklisting?

Microsoft SNDS (Smart Network Data Services) isn't a blocklist - it's a visibility tool that shows you how Microsoft perceives your sending IP's reputation specifically for Outlook.com, Hotmail, and Microsoft-hosted mailboxes. Think of it as Microsoft's report card on your sender behavior.

What SNDS shows:

• IP status: Green (good), Yellow (moderate), Red (poor reputation)
• Spam filtering data: Percentage of your mail filtered as spam
• Trap hits: Whether you've hit Microsoft's spam traps
• Complaint data: Spam complaints from Microsoft users
• Volume data: How much mail you're sending to Microsoft recipients

How SNDS relates to blocking:

• Red status typically means your mail is being heavily filtered or blocked
• SNDS data reflects internal Microsoft reputation, not external blocklists
• You can be blocked by Microsoft even with clean Spamhaus status
• Conversely, Microsoft might accept your mail even if minor blocklists flag you

How to access:

1. Visit postmaster.live.com/snds
2. Sign in with a Microsoft account
3. Verify ownership of your IP ranges
4. View reputation data for your sending IPs

When you're blocked by Microsoft:

• SNDS status will typically show Red
• You may see 550 errors referencing "jmrp" or "SNDS" in bounces
• Use the JMRP (Junk Mail Reporting Program) to get feedback on spam reports
• Submit a support request through the SNDS portal for severe blocking

Remediation:

• Reduce complaint rates by improving targeting and consent
• Clean lists to remove inactive and trap addresses
• Ensure proper authentication (SPF, DKIM, DMARC)
• Consider re-warming the IP with engaged segments

SNDS is Microsoft showing you your permanent record. Unlike external blocklists you can look up anywhere, this is the view from inside the castle - and if those gates are closed, you need to negotiate directly with the gatekeeper.