How to Check Your Email Sender Reputation Every Week

You check your email sender reputation with three free tools and your own campaign numbers. Google Postmaster Tools shows how Gmail treats your sending domain: spam rate, authentication, delivery errors and, for now, a reputation tier from High to Bad.

Microsoft SNDS shows how Outlook.com's filters treat the IP addresses you own. A blocklist lookup such as MXToolbox tells you whether a sending IP sits on a public blacklist.

None of them tells you where your last email landed. Each one is a delayed, partial reading from one provider. Postmaster Tools only counts mail sent to personal @gmail.com addresses. SNDS only opens up for IPs you can prove you control.

So a real check is a weekly routine across all of them, read next to your own bounce and reply numbers.

Why I look at the dashboards last

Every tool in this article reports on something that already happened. Postmaster's spam rate is complaints you have already received. A red day in SNDS is yesterday's filtering. By the time a domain drops to Low, the prospects on that domain stopped seeing you some time ago.

So the rules that protect a sender reputation come before any dashboard. Smirnov Consulting Group is a Prague-based B2B outbound lead generation agency that runs cold email and LinkedIn campaigns for founder-led B2B companies and books qualified sales calls. Every account we send from answers to three rules, no exceptions:

• Authentication (SPF, DKIM and DMARC) has to be live before a single message goes out at volume.
• I pull a list the moment its bounces cross the 0.5% line.
• Volume only goes up once warm-up is behind us, not while it is still running.

Plenty of deliverability guides let bounces run to 2%. I would rather stop a list at 0.5% than find out at 2% what the list did to the domain. The dashboards below tell me whether those three rules held. They cannot replace them.

What does Google Postmaster Tools show?

Postmaster Tools is Google's dashboard for anyone sending to Gmail. You add your sending domain, copy a TXT or CNAME record into your DNS, and Google usually verifies it right away, though the status can take up to 10 minutes to update (Google Workspace Admin Help).

Google lists eight dashboards: Compliance status, Spam rate, IP Reputation, Domain Reputation, Feedback loop, Authentication, Encryption and Delivery errors (Postmaster Tools dashboards). For a cold email sender, four of them matter every week.

Spam rate. The share of your mail that recipients marked as spam by hand. Gmail's sender guidelines ask every sender to stay below 0.3% and recommend staying below 0.10% (Gmail sender guidelines, checked September 2026).

Authentication. The percentage of your mail that passes SPF, DKIM and DMARC. Anything short of a full pass means a DNS record broke or a sending tool is signing wrong.

Compliance status. Whether you meet Google's sender requirements, in one view.

Domain and IP Reputation. Four tiers. In Google's own definitions, High means spam rates have stayed very low and Gmail rarely flags the mail. Medium means occasional spam and fair deliverability. Low means mail "is likely to be marked as spam". At the Bad tier, Google's guidance says a sender should expect Gmail to reject or spam-folder nearly everything it receives from that domain or IP.

Use the tiers while you can. Google's note on the move to Postmaster Tools v2 says every old dashboard carries over except Domain and IP Reputation, which are going away. On timing, it only tells senders to "stay tuned" (Google's v2 transition note, checked September 2026).

Build your routine on spam rate, authentication and compliance, so nothing breaks the week the tiers disappear.

What Postmaster Tools cannot see

It only counts personal Gmail recipients. Google says the data applies to messages sent to a personal @gmail.com or @googlemail.com inbox, nothing else. Mail to a prospect at a company domain hosted on Google Workspace does not count. In B2B, where most of your list sits on company domains, that slice can be small.

It hides low volume. If too few messages reach Gmail on a given day, Google withholds the data to protect user privacy and shows "No data found". A fresh domain sending a few dozen emails a day, mostly to company addresses, may show nothing at all. That is not a clean bill of health. It is missing data.

It is late. Google says its dashboards usually update within 24 hours, sometimes later, and a fix to your compliance can take up to 7 days to show.

It misses mail Gmail filtered on its own. One deliverability vendor's analysis says the spam rate only counts authenticated mail that reached an engaged recipient's inbox before being marked as spam (Suped's analysis, vendor content). Mail Gmail filtered to spam on its own never enters that number. A low spam rate and a spam-folder problem can exist at the same time.

What does Microsoft SNDS show?

SNDS (Smart Network Data Services) is Microsoft's data feed on how Outlook.com treats your sending IPs. You sign in with a Microsoft account, request access to the IPs you are responsible for, and pass an authorization step.

Access expires 10 months after approval and you have to reattest ownership (Microsoft SNDS, checked September 2026). Microsoft's own line on that page: "Reputation is always the responsibility of the sender."

Per IP, per day, SNDS shows recipient counts, a filter result, complaint reports and a few security flags such as open proxy status. The filter result is a color, and Microsoft defines it plainly (SNDS FAQ):

Data is aggregated once a day, around midnight Pacific time, for the day before, and kept for 90 days.

What SNDS cannot see

It has no domain view. SNDS is built around IPs. Microsoft says the filter result does not directly represent what reached inboxes or Junk folders, because user settings can rescue some mail.

Green is a wide band. An IP where Microsoft judged 9% of the mail as spam is still green. For cold email, having 9% of your mail judged as spam is already a real problem.

Shared IPs mix you with everyone else. Microsoft notes that behind a shared IP you see all the complaints, whatever domain sent the mail.

Sending through a Google or Microsoft mailbox locks you out. Microsoft aims SNDS at people who own IP space. Cold email sent from Google Workspace or Microsoft 365 mailboxes goes out on IPs that belong to Google or Microsoft. You have nothing to claim.

For you, SNDS is a closed door, and that is fine: your Outlook signal comes from bounces, replies and placement tests.

The free sender reputation tools compared

Read the last row first. It is the only one built from your actual prospects. The four tools above it explain why those numbers moved.

The weekly check, step by step

Pick one day a week and one sheet with a row per sending domain. Then work through it in this order.

1. Bounce rate per mailbox, last 7 days. Anything at or above 0.5% means the list is the problem. Pause that list and re-verify it before it touches the domain again. How fast a list decays into bounces, and when to re-verify it is its own topic.
2. Replies per mailbox. You are looking for one domain falling while the others hold. A sudden drop while bounces stay normal usually points at placement.
3. Postmaster spam rate, per domain. Under 0.10% is fine. Between 0.10% and 0.3%, slow that domain down and look at who you are targeting. At 0.3% or above, stop it.
4. Postmaster authentication. SPF, DKIM and DMARC should all pass. If one dropped, fix the DNS record before the next send.
5. Postmaster reputation and compliance. Note the tier while it exists. "No data found" at low volume is normal; write "no data" in the sheet and move on.
6. SNDS, only if you own the sending IPs. Anything yellow or red gets looked at the same day.
7. Blocklist lookup on every sending IP and domain. A new listing moves that domain out of the routine and into recovery.
8. Volume decision. Raise volume on a domain only after warm-up is done and the readings above stayed clean. Never the other way round.

Write one line per domain: date, bounce rate, spam rate, tier, authentication, listing yes or no. One week tells you little. Four weeks in a row show you a trend.

How do you monitor 10 or 20 sending domains at once?

The tools are built for one domain at a time. Real cold email is not. The sending setup I use is 10-20 domains and 20-40 email accounts, SPF, DKIM and DMARC on every one, and each account warmed up for 10-14 days minimum before volume goes up.

That changes the routine in three ways.

Every domain gets verified in Postmaster Tools on day one. One DNS record each. Adding them later, after a problem, means you have no history to compare against.

You compare domains against each other. This is the one thing no single dashboard gives you. If one domain drifts while the rest hold, the cause sits with that domain: its list segment, its copy variant, its mailboxes. If all of them drift in the same week, the cause is shared, such as a new list source or a new sequence.

One bad domain does not stop the campaign. Spreading volume across many domains is what lets you rest one while the others keep sending. Pull its mailboxes and look at what that domain did differently.

Which readings mean stop sending?

The last row is the one people skip. When every tool looks healthy and replies still drop, check inbox placement rates by provider and work through what actually moves a cold email out of spam. The dashboards only report what each provider chooses to share.