Microsoft SNDS: the deliverability tool nobody reads correctly
Smart Network Data Services exposes the complaint and trap data Outlook.com uses to filter you. Here is what each column means and the thresholds that actually matter.
Microsoft's Smart Network Data Services (SNDS) is the only window most senders ever get into Outlook.com filtering. It is free, frequently updated, and almost always misread — usually because the column names are terse and the documentation is spread across three different help portals.
What each SNDS column means
| Column | What it shows | Threshold to worry |
|---|---|---|
| RCPT commands | Total recipients attempted | Context for ratios |
| Data commands | Messages actually transferred | Should match RCPT |
| Message recipients | Unique recipients reached | — |
| Filter result | GREEN/YELLOW/RED bucket | Anything but GREEN |
| Complaint rate | % of recipients who hit 'Junk' | Above 0.1% |
| Trap message period | Window when traps were hit | Any non-empty value |
| Trap hits | Spam-trap addresses contacted | 1 or more |
| Sample HELO | EHLO/HELO string used | Should match rDNS |
| Sample MAIL FROM | Return-path used | Should be on a domain you control |
The three SNDS warning signs
- Filter result flips to YELLOW. You have ~72 hours before delivery degrades. Pause campaign volume and identify the offending segment.
- Trap hits appear for the first time. A trap is an address that should never receive mail — hitting one means your acquisition or hygiene process is broken.
- HELO/MAIL FROM mismatch with rDNS. Microsoft penalizes infrastructure that does not reverse-resolve cleanly to its sending identity.
Pairing SNDS with JMRP
SNDS gives you the rate; JMRP (the Junk Mail Reporting Program) gives you the addresses. Sign up at the same portal, register a complaint-handling mailbox, and Microsoft will forward every 'Junk' click. Suppress those addresses immediately — continuing to mail them after a complaint is the fastest way to a permanent block.
Frequently asked questions
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