Postmaster tools: what Google, Microsoft and Yahoo show to senders

The large mailbox providers give senders dashboards that expose part of what they observe about a domain or an IP range: reputation, complaint rate, delivery errors, authentication. These tools are free, deliberately limited, and indispensable as soon as a domain sends any volume to their users.

Google Postmaster Tools#

Google Postmaster Tools (postmaster.google.com) covers traffic received by Gmail and by Google Workspace mailboxes. Enrolment is per domain: control of the domain is proved by publishing a TXT or CNAME record supplied by the tool. Data only appears above an unpublished minimum daily volume, in the region of a few hundred authenticated messages.

The available metrics:

• Spam rate: the share of messages delivered to the inbox and then reported as spam. Google asks senders to stay below 0.3% and aims for 0.1%.
• Domain reputation and IP reputation: four levels (bad, low, medium, high), computed from authenticated traffic. A drop from "high" to "medium" usually precedes spam-folder placement.
• Authentication: the share of traffic passing SPF, DKIM and DMARC. A gap between DKIM and DMARC reveals an alignment problem.
• Encryption: the share of traffic received over TLS.
• Delivery errors: reasons for rejection, grouped by category (IP reputation, DMARC policy, content and so on).

A redesigned version of the dashboards, rolled out from 2024, adds a compliance status against the sender requirements, flagging directly the domains that miss the required complaint rate or authentication.

The spam rate shown by Google is the only information of its kind available for Gmail, which does not offer an individual feedback loop. Values are aggregated per day and may be missing on low-volume days.

Microsoft SNDS#

Smart Network Data Services (sendersupport.olc.protection.outlook.com/snds) covers Outlook.com, Hotmail and Live mailboxes. Enrolment is per IP range rather than per domain: access is requested for a range, then confirmed through a contact address tied to the block (the abuse or postmaster contact in WHOIS, or the postmaster@ address of the reverse DNS name).

For each IP and each day, SNDS shows:

• the number of messages received and the volume of connections;
• a colour (green, yellow, red) reflecting the complaint and spam-trap rate;
• the complaint rate and the number of deliveries to spam traps;
• the IP's activity window and the filter verdict.

SNDS only shows data from roughly a hundred messages per day per IP. It is complemented by the Junk Mail Reporting Program (JMRP), Microsoft's feedback loop, which returns a copy of messages reported by users. Since 2025, Microsoft has in turn applied authentication requirements to senders of more than 5,000 messages a day, visible in SMTP rejections rather than in SNDS.

Yahoo Sender Hub#

Yahoo gathers its sender resources in the Sender Hub (senders.yahooinc.com), which covers Yahoo Mail, AOL and the associated brands. The site publishes the sender requirements, the SMTP error codes and their meaning, a form to request unblocking, and enrolment in the feedback loop (Complaint Feedback Loop), which is based on the DKIM signing domain.

Yahoo does not offer a reputation dashboard comparable to Google's. The useful indicators come from the feedback loop (individual complaints in ARF format), from the aggregate DMARC reports Yahoo sends daily, and from the SMTP rejection texts, such as 421 4.7.0 [TSS04] (temporary throttling for reputation reasons) or 554 5.7.9 (rejection related to authentication).

Reading these tools together#

None of these tools gives a complete picture; each one describes only the traffic received by its own provider. A useful reading cross-checks:

1. the Google and Microsoft complaint rates against the complaints received through feedback loops (Yahoo, Microsoft);
2. the reputation levels against the 4xx and 5xx codes recorded in the MTA logs for the same destinations;
3. the displayed authentication rates against the aggregate DMARC reports, to pinpoint the unaligned stream;
4. the dates: a reputation drop usually appears one or two days after the campaign that caused it.

What to check#

• Every sending domain, including subdomains dedicated to marketing or transactional mail, is enrolled in Google Postmaster Tools.
• Every sending IP range, including a provider's ranges when the provider grants access, is registered in SNDS.
• The Yahoo feedback loop is active for every DKIM signing domain.
• Access is shared among several people and does not depend on one individual account.
• Data is collected regularly, daily for instance, to keep a history beyond the window the dashboards display.

Common mistakes#

• Enrolling the main domain but not the subdomain that actually sends, so the data stays empty.
• Expecting data for a low-volume domain: below the threshold the dashboards stay empty, and that is not a problem in itself.
• Reading a complaint rate on a single low-volume day, when two complaints are enough to exceed 0.3%.
• Confusing the IP reputation shown by Google with the one computed by Microsoft: the two providers share nothing.
• Concluding from a green SNDS that everything is fine at Gmail, or the reverse.

Further reading#

Provider dashboards describe the recent past, without alerts and without correlation to the sending itself. To check concretely how a message is received and authenticated before a bulk send, Postmastery offers a service to test an email and its sending infrastructure.