Google Postmaster Tools

Google Postmaster Tools (https://postmaster.google.com/ — sign-in with a Google account required) is Google's free monitoring console for senders. After verifying domain ownership, a sender gets dashboards on spam rate, IP/domain reputation, authentication success, encryption, delivery errors, feedback-loop data, and compliance with the Gmail sender requirements.

All data covers mail to personal Gmail accounts only (@gmail.com / @googlemail.com) — not Google Workspace recipients.

Enrollment

Prerequisites: a Google or Google Workspace account; the domain added must be the DKIM d= domain or the SPF (Return-Path) domain used to authenticate your mail.

1. Add the domain: sign in at postmaster.google.com, click Add, enter the authentication domain.
2. Verify ownership: copy the provided TXT record into the domain's DNS, then click Verify. Usually instant, up to ~10 minutes. Dashboards show no data until verified.
3. Grant access (optional): Manage Domains > More > Manage > Add a Google email address. Read access can be shared; the grantee is not notified automatically.

Common issues: verification failures from DNS propagation delay or a mistyped record (retry, or generate a new string); access grants require the grantee to have a Google account; missing dashboard data usually means volume is too low (privacy threshold).

Data characteristics

• Updated daily, typically within 24 hours (compliance status can take up to 7 days to reflect changes).
• Timestamps are UTC.
• Selectable ranges: 7, 30, 60, 90, or 120 days.
• Days with low volume are omitted to protect user privacy — gaps don't mean zero.
• Google attempts to exclude forwarded messages from the data, but some may leak into dashboards.
• Unauthenticated mail is largely invisible: most dashboards only cover mail that passed SPF or DKIM for the verified domain.

Dashboards

Compliance status

Checks each Email Sender Guidelines requirement and rates it Compliant, Needs work, or No data found (insufficient volume). Items checked for all senders: SPF/DKIM authentication, DNS (PTR) records, message formatting, TLS encryption, user-reported spam rate. Additional items for bulk senders (~5,000+/day): DMARC, one-click unsubscribe support, and honoring unsubscribes. Compliance is displayed for the primary domain, but both primary-domain and subdomain traffic feed the calculation. Allow up to 7 days after a fix.

Spam rate

The percentage of your delivered mail that Gmail users manually mark as spam, per day. Targets: stay below 0.10%, never reach 0.30% (threshold details). Critical interpretation caveat: the denominator is inbox-delivered mail — "if Gmail automatically sends a significant number of your messages to spam, the rate shown in the dashboard might seem low." A low spam rate with poor inbox placement is therefore possible; read this dashboard together with reputation.

IP reputation and Domain reputation

Four tiers, same scale for both dashboards:

Tier	Meaning
High	Very low spam rate; complies with Gmail's sender guidelines; mail rarely filtered
Medium	Known to send legitimate mail with occasional low-volume spam; fair deliverability
Low	Significant history of sending spam; mail likely marked as spam
Bad	High spam volume; mail nearly always marked as spam or rejected at SMTP time

Domain reputation covers only messages authenticated with the exact verified DKIM/SPF domain. Reputation recovery takes time — sustained compliant sending, no shortcuts. The two dashboards separate infrastructure problems (IP) from brand/content problems (domain); see advanced IP segmentation for using this separation deliberately.

Feedback loop (FBL)

Gmail's FBL is aggregate, not per-message: it does not return individual complaint reports. Instead, senders embed a Feedback-ID: header and Postmaster Tools reports the average spam rate per identifier per day plus the volume of unique identifiers flagged.

Header format:

Feedback-ID: a:b:c:SenderId

• SenderId (rightmost field): mandatory, 5–15 characters, unique and consistent per sender.
• a, b, c: up to three optional custom fields (campaign, customer, mail stream, …). Data is aggregated for the first 4 colon-separated fields counted from the right.
• Don't reuse the same identifier value in different fields (aggregates would mix); don't use per-message values like a Message-ID (each identifier needs enough daily volume and distinct spam reports to produce data).

Requirements for FBL data: traffic DKIM-signed by a domain you control, that domain verified in Postmaster Tools, sending IPs in the SPF record with valid PTR records. Dashboard views: by From: header domain, or by all DKIM-signing domains. FBL data covers @gmail.com recipients only. Primary use case: pinpointing which campaign/customer/stream drives complaints — especially for ESPs whose customers share domains.

Authentication

Percentage of attempted mail that passed SPF, DKIM, and DMARC, per day. Correctly configured senders typically reach ≥95% success for DKIM and DMARC. SPF rates run naturally lower — third-party/forwarded delivery breaks SPF (a path-based check; see DMARC). Domains that don't send mail show no results.

Low-rate debugging: for DKIM, check TXT record formatting, key correctness, and DNS TTL/expiration; for SPF, check record syntax and that every authorized sending IP/service is listed; for DMARC, ensure SPF/DKIM pass first and consider relaxed alignment.

Encryption

Percentage of inbound TLS (your mail arriving at Gmail over TLS) and outbound TLS traffic. TLS is a hard requirement of the sender guidelines; this should be at/near 100%.

Delivery errors

Percentage of authenticated mail that was rejected or temporarily failed, versus all authenticated mail, with error-reason breakdowns:

Error reason	Typical cause	Action
Rate limit exceeded	Suspiciously high sending rate	Pause, then resume slowly (re-warm up)
Suspected spam	Message classified as likely spam	Usually low reputation; escalate via bulk-sender form if it persists on compliant mail
Email content is possibly spammy	Content flagged	Review content; escalation form if needed
Bad or unsupported attachment	Blocked file type	Send only Gmail-supported attachment types
DMARC policy of the sender domain	Your own DMARC p=reject/quarantine rejecting your mail	Check DMARC aggregate reports; consider p=none while fixing alignment
Low IP reputation / Low domain reputation	Poor reputation tier	Fix root cause, rebuild reputation
IP in one or more public RBLs / Domain in RBLs	Public blocklist listing	Request delisting from the blocklist operator
PTR record missing	No reverse DNS	Add a PTR record (verify with Google Admin Toolbox Dig)

Temporary failures are throttling: "completely stop sending for a short period of time, then resume sending at a slower rate." Specific SMTP codes are cataloged in Gmail troubleshooting.

Fit in a deliverability workflow

1. Enroll every authentication domain (DKIM d= and SPF Return-Path domains) before problems occur — there is no retroactive data.
2. Daily: watch spam rate against 0.10%/0.30% and both reputation tiers.
3. Per campaign: use Feedback-ID + FBL to attribute complaints to streams/customers/campaigns.
4. On delivery incidents: correlate Delivery Errors reasons with SMTP logs, check Authentication and Encryption dashboards for regressions.
5. For compliance: verify all items in Compliance Status; only compliant senders with <0.3% spam rate over 7 consecutive days qualify for Google mitigation.

Google's accompanying list-hygiene recommendations: send only to opted-in recipients, confirm addresses at signup (confirmed opt-in), periodically reconfirm interest, stop mailing non-engagers, and make unsubscribing trivial.

Yahoo offers analogous facilities — see Yahoo complaint feedback loop and Yahoo performance feeds.