Microsoft Smart Network Data Services (SNDS) is a free monitoring tool from Outlook.com that shows how Microsoft evaluates the reputation and activity of your sending IP addresses. It reports mail volume, spam-complaint rates, spam-trap hits, and a filter-result status for each IP, which together explain why your mail lands in the Outlook, Hotmail, Live, and MSN inbox or the junk folder. If Gmail has Postmaster Tools, Microsoft has SNDS, and any serious sender should watch both.
Reads public DNS only. Nothing is stored unless you save the domain to an account.
What SNDS is and what it measures
SNDS is IP-centric, not domain-centric. You register the individual IP addresses you send from, Microsoft verifies that you control them, and it then surfaces the same signals its own filters use to decide inbox placement. It does not tell you about specific messages or recipients, and it does not read your DKIM or DMARC results. For authentication signals you need DMARC aggregate reports and the Authentication-Results header instead. SNDS answers a narrower question: from Microsoft's point of view, is this IP a trustworthy source of mail right now?
Because it is IP-based, SNDS reflects the reputation of whatever infrastructure you send through. On a dedicated IP the data is entirely yours. On a shared pool it reflects every sender on that IP, which is one reason the dedicated versus shared IP decision matters. If you understand the distinction between domain reputation and IP reputation, SNDS is your window into the IP half.
Reading the SNDS data columns
The core SNDS report is a table with one row per day per IP. Each column is a filter signal. Read them together rather than fixating on any single number.
| Column | What it shows | What good looks like |
|---|---|---|
| Activity | Mail volume band Microsoft observed from the IP over 24 hours | Steady, matching your actual sending |
| RCPT commands | Count of RCPT TO commands, one per addressed recipient | Consistent with your list size |
| DATA commands | Count of accepted message bodies | Close to RCPT count |
| Filter result | Green, yellow, or red status for the IP | Green |
| Complaint rate | Share of delivered mail marked as junk | Under 0.3%, ideally under 0.1% |
| Trap message period | First and last time the IP hit a spam trap in the window | Blank |
| Sample HELO | The HELO/EHLO name the IP announced | Your real, stable hostname |
Activity, RCPT, and DATA
Microsoft shows mail volume as a band (from None through Very High) rather than exact counts, to protect its own traffic data. The RCPT and DATA columns come straight from the SMTP conversation. RCPT TO is issued once per recipient, and DATA marks an accepted message body. A large gap between the two, where you attempt many recipients but few messages are accepted, points to blocking or throttling upstream. A sudden volume spike that does not match your sending is a strong sign the IP is compromised or that a shared neighbor is sending badly.
Filter result: the traffic light
The filter result is the headline metric, expressed as a color:
- Green means mail from the IP is delivered normally with low filtering.
- Yellow means the IP faces heightened filtering, and a meaningful portion of mail is being routed to junk.
- Red means severe filtering, with most messages junked or blocked outright.
Yellow generally maps to throttling and red to blocking. If you see red, treat it as an active incident and stop increasing volume until it clears.
Complaint rate
The complaint rate is the percentage of delivered mail that Outlook users marked as junk. Microsoft's published guidance, echoed in the 2026 bulk sender requirements, is to keep complaints below 0.3%, and a rate under 0.1% is where healthy senders sit. Sustained complaint rates above the threshold push the filter result toward yellow and then red. Complaints are the fastest way to wreck Outlook reputation, so this column deserves daily attention.
Trap message period
If the IP sent mail to one of Microsoft's spam traps, SNDS records the first and last trap hit in a Trap message period. Traps are addresses that should never receive legitimate mail, so any hit signals a list-hygiene failure: purchased data, scraped addresses, or stale contacts that decayed into traps. Trap hits cause rapid reputation deterioration, and the target is always zero. If you see a trap period, review how those addresses entered your list. The guide on what a spam trap is covers the common sources and how to purge them.
Sample HELO
SNDS shows a sample of the HELO/EHLO hostname your server announced. It should be a stable, real hostname that matches your reverse DNS. A mismatched or generic HELO undermines trust and often correlates with a missing or misconfigured PTR record, which Microsoft weighs heavily.
How to enroll in SNDS
Enrollment is free but requires proving you control each IP.
- Sign in with a Microsoft account, then request access by listing the specific IP addresses or CIDR ranges you send from. You add IPs individually or as ranges.
- Microsoft looks up the WHOIS and DNS records for each IP and sends a verification link to the standard administrative contacts for that IP, typically
abuse@orpostmaster@for the netblock owner. - Confirm the link. Verification is one-time per IP.
- Wait for data to populate. Rows appear only after the IP sends enough mail for Microsoft to observe.
If you send through an ESP such as Amazon SES, SendGrid, or Mailgun, the ESP owns the IPs and therefore controls verification. Many ESPs enroll their ranges and either forward you the data or expose it in their dashboard. On a dedicated IP, ask your provider to forward the verification message so you can claim your own SNDS view.
Enroll in JMRP as well
SNDS tells you the complaint rate, but it will not tell you which recipients complained. That is the job of the Junk Mail Reporting Program (JMRP), Microsoft's complaint feedback loop. When an Outlook user clicks Junk, JMRP forwards a copy of that message, in Abuse Reporting Format (ARF), to an address you designate. You then suppress those recipients immediately.
Enroll separately from SNDS, starting at the same Microsoft postmaster site. You register your IPs and a Hotmail, Live, or Outlook.com account to receive reports, and Microsoft verifies IP ownership the same way. Run SNDS and JMRP together: SNDS shows the trend, and JMRP gives you the individual addresses to remove. Suppressing complainers on the same day is the single most effective way to keep the SNDS complaint column under control.
Using SNDS to fix Outlook and Hotmail delivery
When Outlook or Hotmail delivery drops, work through SNDS in order:
- Filter result is yellow or red. Reduce volume, then find the driver in the other columns. Do not keep pushing your normal send rate into a red IP.
- Complaint rate is climbing. Tighten opt-in, honor the List-Unsubscribe header with one-click unsubscribe per RFC 8058, and use JMRP output to remove complainers same-day. High complaints are the most common cause of Outlook junking.
- Trap message period is populated. Stop sending to unengaged segments and re-verify how addresses entered the list. Traps almost always mean stale or acquired data.
- HELO or reverse DNS looks wrong. Fix the PTR record so it is forward-confirmed and matches your HELO.
- The IP is new. Low volume plus cautious filtering is normal. Warm the IP up by raising volume gradually over several weeks.
SNDS is diagnostic, not corrective. It shows the symptom, but the fix is always on your side: authentication, list hygiene, and complaint handling. Confirm your SPF, DKIM, and DMARC pass before blaming reputation, because unauthenticated mail is filtered regardless of IP history. SNDS is one instrument in the broader picture of sender reputation, and it complements what Google Postmaster Tools shows you on the Gmail side.
SNDS and Postmaster Tools side by side
| Microsoft SNDS | Google Postmaster Tools | |
|---|---|---|
| Keyed on | Sending IP address | Sending domain |
| Mailboxes covered | Outlook, Hotmail, Live, MSN | Gmail, Google Workspace |
| Complaint detail | Rate only (addresses via JMRP) | Rate only (no per-address feedback loop) |
| Reputation view | Filter result color per IP | IP and domain reputation bands |
| Enrollment | IP verification via WHOIS contact | DNS TXT verification of the domain |
Use both. Delivery problems are rarely universal. An IP can be green at Microsoft and poor at Gmail, or the reverse, and only side-by-side monitoring tells you which mailbox provider is unhappy.
Frequently asked questions
How long does SNDS data take to appear?
After you verify an IP, rows appear only once Microsoft observes enough mail from it, usually within a day or two of meaningful sending. Very low-volume IPs may show sparse or delayed data because Microsoft needs a sample large enough to report on.
Is SNDS the same as Microsoft Postmaster Tools?
No. SNDS reports IP-level activity and reputation and is the long-standing tool for senders. Microsoft has also offered a separate Postmaster Tools interface, but SNDS remains the primary source for per-IP filter result, complaint rate, and trap data. JMRP is the complaint feedback loop and is separate from both.
Can SNDS tell me who marked my email as spam?
No. SNDS shows only the aggregate complaint rate. To see the individual recipients who complained, enroll in the Junk Mail Reporting Program (JMRP), which forwards each junk report as an ARF message so you can suppress those addresses.
Do I need a dedicated IP to use SNDS?
No, but the data is only as useful as your control over the IP. On a shared pool the figures reflect every sender, so a neighbor's bad behavior can turn your filter result yellow. On a dedicated IP the numbers are entirely yours and far more actionable.
Before you go chasing Outlook reputation, make sure the fundamentals pass. Run a free SPF, DKIM, and DMARC check with SPFWise to confirm your mail is authenticated and aligned, then use SNDS and JMRP to keep your Outlook and Hotmail delivery healthy.