Operations
US email deliverability: Google Postmaster Tools and Microsoft SNDS explained
What Google Postmaster Tools and Microsoft SNDS report, how their data differs, and how US senders should read spam rate, reputation and compliance signals.
What each tool tells you
- Google Postmaster Tools shows how Gmail sees your domainspam rate, domain and IP reputation, authentication, encryption, delivery errors and a compliance status. It covers mail sent to personal Gmail accounts only.
- Microsoft SNDS (Smart Network Data Services) gives IP-level data on how Outlook.com users rate your mail. It is tied to the IP addresses you are responsible for, not to a domain.
- Neither tool is real time. Treat them as trend lines and review them weekly, not after each send.
- The two tools answer different questions. Postmaster Tools is the better guide to domain behavior and sender-guideline compliance, and SNDS is the better guide to what a sending IP looks like to Microsoft.
Why US senders need both
Gmail and Outlook.com handle a large share of consumer mailboxes, and each publishes its own rules for bulk senders. A journey can look healthy in your email platform's reports while one of these providers is filtering it, because delivered in a platform report only means the receiving server accepted the message. Postmaster Tools and SNDS are the two places where the mailbox providers show their own view.
Both tools sit alongside the legal basics in CAN-SPAM for US subscriber journeys. CAN-SPAM sets what a message must contain. The provider tools show whether recipients and filters accept it.
Google Postmaster Tools: the dashboards
Google lists these dashboards in its help center, and each one reads a different part of your mail.
| Dashboard | What it shows |
|---|---|
| Compliance status | Your standing against Google's sender requirements, with each item marked Compliant, Needs work or No data found |
| Spam rate | The percent of DKIM-authenticated messages that recipients marked as spam after they reached the inbox |
| IP reputation | A quality rating for the IP addresses you send from |
| Domain reputation | A quality rating for your sending domains, counting only mail from the exact domain used for DKIM and SPF authentication |
| Feedback loop | Spam rates for campaigns that carry a feedback loop ID, once you set it up |
| Authentication | The percent of messages that pass SPF, DKIM and DMARC |
| Encryption | The percent of authenticated messages sent over TLS |
| Delivery errors | The percent of authenticated messages that were rejected or temporarily failed, with reasons |
Reputation uses four categories: Bad, Low, Medium and High. Google describes High as a history of very low spam rates and compliance with Gmail's sender guidelines.
Data limits that catch people out
- Low-volume days may be missing from the dashboards. Feedback loop IDs appear only after a minimum number of spam reports, and compliance can show No data found when there are not enough emails to evaluate.
- Data is typically updated within 24 hours but can take longer.
- Compliance uses a rolling average, so a fix can take up to 7 days to show.
- Times are in UTC. Date ranges run from 7 to 120 days.
- Spam rate counts only DKIM-authenticated messages, so an unsigned stream will not appear in it at all.
The numbers Google asks senders to hold
Google's sender guidelines give these figures:
- Keep the user-reported spam rate below 0.1%.
- Never let it reach 0.3% or higher. Above that, a bulk sender cannot get mitigation for delivery issues, and eligibility returns only after the rate stays under 0.3% for 7 consecutive days.
- A bulk sender is one that sends close to 5,000 messages to personal Gmail accounts in 24 hours, counting all mail from the same primary domain. That status is permanent.
- All senders must authenticate with SPF and DKIM. Bulk senders must also publish DMARC with at least
p=none, align the From domain with SPF or DKIM, and support one-click unsubscribe on marketing mail using List-Unsubscribe headers under RFC 8058. Google recommends honoring unsubscribe requests within 48 hours.
For a subscriber journey, that last point matters more than it looks. A welcome, nurture or re-engagement flow that sends a promotional message without a working one-click header can fail the compliance panel even when spam rate is low.
Microsoft SNDS: what it is and what it is not
Microsoft describes SNDS as a free service that gives high-level insight into how Outlook.com users rate the email they receive and the health of your IP space. Its own pages say it shows how many users complained about your email, and that it can help you spot compromised servers, malware and botnets. To use it, sign in with a Microsoft account and request access to the IPs you are responsible for.
Three practical consequences follow.
- It is IP-based.If you send through an email platform on shared IP addresses that you do not control, you may not be able to request access, and the platform is the party that sees the data. Ask the provider what it sees for your traffic.
- Access expires.Microsoft says network access expires 10 months after approval or migration, and it sends reminders to reattest ownership. Put the date in a calendar, or the data simply disappears.
- It sits next to JMRP.The Junk Email Reporting Program is a free service that sends select message headers for emails that Outlook.com users mark as junk. Microsoft says enrollment is through SNDS and feedback typically arrives within as little as 72 hours. For list hygiene, JMRP reports tell you which addresses to suppress.
Microsoft's rules for high-volume senders
Microsoft's policy page states that, from May 5, 2025, domains sending more than 5,000 emails per day to Outlook.com accounts must be fully compliant with SPF, DKIM and DMARC. Non-compliant messages go to the junk folder and may be rejected with 550 5.7.515. The DMARC policy must be at least p=none, with p=reject recommended, and must align with SPF or DKIM.
The same page asks senders not to retransmit after a permanent failure, to stop sending to a recipient after multiple non-delivery responses, to use valid reverse DNS and to make the unsubscribe mechanism clearly documented and easy to use. It does not publish a complaint-rate threshold, which is why a number from a blog post should not be treated as Microsoft policy.
Reading rejections and blocks
Microsoft's troubleshooting page lists specific SMTP responses, and several map directly to a fix:
- 550 5.7.515:authentication is missing for a domain above 5,000 emails per day. Implement SPF, DKIM and DMARC.
- 550 SC-004:the IP is blocked because of complaints. Microsoft's remedy is to enroll in JMRP and remove unwanted recipients.
- 421 RP-001, RP-002 and RP-003:rate or connection limits tied to reputation. Reduce volume and improve complaint rates and list accuracy.
- 550 SC-002:the IP showed namespace mining behavior, meaning address checking without sending real mail. Stop doing it and check for compromised accounts.
Microsoft also says that submitting a support request does not guarantee delivery.
A weekly review routine
- Check Google compliance status first.Fix any item marked Needs work, starting with authentication and unsubscribe.
- Read the spam rate trend, not a single day.Compare 7-day and 30-day views against 0.1% and 0.3%.
- Match spikes to sends.Tie any change to a specific journey stage or segment using your sending log. The deliverability checklist lists what to record for each send.
- Check SNDS and JMRP for the same dates.A complaint pattern that shows in both providers points to a list or content problem, not a one-provider quirk.
- Suppress and fix upstream.Remove complainers, re-check acquisition sources, and review the common deliverability questions if a pattern persists.
For a wider plan, see how to improve email deliverability.
Limits of these tools
Neither tool shows inbox placement. A message can be accepted and still land in a junk folder, Google says its dashboards may omit low-volume days, and Postmaster Tools covers personal Gmail accounts only. Read both as signals of reputation, then confirm with seed tests and your own engagement data.
