Sender Reputation Check for B2B Teams: Which Surfaces Can Actually See You
Most sender reputation tools score an IP address, and if you send from Google Workspace that IP is not yours. Which layer you actually control.
Sender reputation covers three layers: IP reputation, which belongs to whoever owns the sending address, domain reputation, which is scoped to your authenticated domain, and per-mailbox signals with no public surface. A team sending from provider mailboxes controls the middle one, and that is where the work belongs.
Key takeaways
- If you send through Google Workspace or Microsoft 365, the sending IPs are shared provider addresses, so an IP reputation score is not measuring your behaviour.
- Several tools ranking for this search are threat intelligence products: EmailRep addresses security analysts working on phishing detection on its own front page.
- Google Postmaster Tools reports on the exact DKIM and SPF authenticated domain, so each sending domain needs its own view rather than one blended figure.
- Microsoft's SNDS reports on IP addresses you control and states that reputation is always the responsibility of the sender, which leaves provider-mailbox senders blind to it.
Reviewed and updated August 13, 2026
Run a sender reputation check and the first thing most tools ask for is an IP address. Paste in the one your mail appears to come from and you get a score, a colour and a verdict. Then you notice the IP belongs to Google or Microsoft, it is shared with every other tenant on that infrastructure, and the score is telling you about their behaviour rather than yours.
That is the central problem with sender reputation for a B2B outbound team. The phrase covers three different things held by different parties at different levels, and the tools that rank for it mostly measure the one level you do not control. Here is what each layer is, which surfaces can actually see you, and what is worth checking every week.
Sender reputation is three things wearing one name
IP reputation is a receiver's opinion of the address the connection came from. It is the oldest form of sender scoring and the one most public tools report on. If you send through Google Workspace or Microsoft 365 mailboxes, the sending IPs belong to the provider, are shared, and are not something you can influence.
Domain reputation is a receiver's opinion of the domain in your authentication. Google's documentation states that its domain reputation dashboard only displays messages sent from the exact domain used for DKIM and SPF authentication, which makes this the layer a cold email programme actually owns.
Mailbox and address level signals are the individual account's history: how much it sends, whether recipients reply, whether it gets marked as spam. This layer has no public surface at all.
For most B2B senders the second one is the only lever, which is why domain reputation is where the attention belongs even though IP reputation is what the free tools report.
- Belongs to whoever owns the sending IP
- Shared across every tenant on provider infrastructure
- Reported by most free lookup tools
- Only actionable if you run your own mail server
- Scoped to the exact DKIM and SPF authenticated domain
- Built from your complaints, bounces and engagement
- Visible in Google Postmaster Tools
- Isolated per domain, so a pool spreads risk
- Per-account sending history and engagement
- Not exposed by any provider dashboard
- Inferred from reply rates and placement tests
- Why one mailbox can underperform its siblings
Half the tools on that search are answering a security question
The results for a sender reputation check mix deliverability surfaces with threat intelligence, and the two are not substitutes.
EmailRep describes its own purpose on its front page as illuminating the reputation behind an email address, and asks visitors directly whether they are a security analyst or researcher working on phishing detection. Cisco's Talos email and spam data sits inside a threat intelligence centre. These are excellent tools for deciding whether an address that just emailed you is dangerous. They are not measuring whether your campaign will reach an inbox.
The practical test for any tool in this category: ask what it would have to see in order to answer your question. Whether your mail lands in the inbox depends on your complaint rate and your recipients' engagement, and no third party has that data. Only the mailbox provider does, and only one of them shows it to you for free.
The surfaces that can actually see you
Google Postmaster Tools is the one authoritative free surface for Gmail delivery, covered in full in Google Postmaster Tools for cold email. It reports domain and IP reputation on a four-level scale, with Google's own definitions: Bad, Low, Medium and High. Two caveats decide whether it helps you. It reports only on the exact authenticated domain, so every sending domain needs its own view. And Google notes the dashboard may not include all data on days when outgoing volume is low, which is precisely the shape of a well built sending pool, so blank panels are common and mean nothing either way.
Microsoft's Smart Network Data Services reports IP-level data and complaint feedback to whoever controls the IP addresses, and states its position on the front page: reputation is always the responsibility of the sender. If you send from Microsoft 365 or Google Workspace mailboxes you do not control those IPs, so SNDS will show you nothing. That is the arrangement working as designed rather than a configuration fault.
Spamhaus publishes a public domain reputation check against its own data. A listing here is one of the few reputation findings with a documented external remedy.
Blocklist aggregators such as MXToolbox check many lists at once, which is the fastest way to find a listing nobody noticed. Reading its output is covered in the MXToolbox deliverability guide.
Seed testing puts your actual message into real mailboxes at each provider and reports placement. It measures inbox placement directly, and its limitation is that a seed list is not your list.
What actually builds it, in the order that matters
A check is only useful if you know what the number is responding to. Receivers do not publish weightings, but the inputs are well established by the providers' own guidance and they are not equally important.
Complaints are the strongest negative signal, because a person pressed a button to say the mail was unwanted. Nothing else in the list is a direct human verdict.
Invalid addresses come next. Hard bounces indicate a list that was not verified, and unverified lists are also the ones that hit spam traps, which is a separate and heavier penalty.
Authentication is a prerequisite rather than a score. Unauthenticated mail is treated as suspicious before behaviour is considered, and Google's requirements tighten at 5,000 messages a day to Gmail accounts, where SPF and DKIM and DMARC all become mandatory rather than advisable.
Volume shape matters more than volume. A domain with a short history sending like an established one looks like a compromised account, which is the pattern receivers are built to catch.
Engagement is the positive signal, and it is the one a cold sender influences least directly and benefits from most. Replies, and messages dragged out of spam, both read as recipients wanting the mail.
Notice what is absent from that list. Nothing about your sending platform, your template design, or your subject line appears in it. Those affect how one message is scored at the filter, and reputation is the accumulated verdict on many messages. That distinction explains why teams who respond to a delivery problem by rewriting copy usually see no change.
The consequence for a team sending from provider mailboxes
Our glossary entry on sender reputation sets out the components and where each one is observable, and it is worth reading before you trust any tool in this category. The consequence specific to cold outbound is short enough to state here.
Your IP reputation is largely somebody else's problem and you cannot fix it. Your domain reputation is entirely yours and is the only component that responds to anything you do. So when a lookup reports a poor IP score for mail sent through Google Workspace, the correct response is to note it and move on rather than to open an investigation, and the correct place to spend the hour is the list.
What a B2B outbound team should check, and how often
The useful checks are the ones tied to a decision.
Weekly, per sending domain: bounce rate, complaint rate and reply rate. These move before any provider rating does, they are yours, and they are per domain, which is the unit reputation is scored in. A blended figure across a pool hides one domain failing while the average holds.
Weekly, automated: blocklist status across every sending domain. Listings are usually found late, and the cost of a listing is proportional to how long it goes unnoticed.
Monthly, or when a trend moves: authentication still passing on every domain, including any added since the last check. New domains added mid-programme are the reliable source of authentication gaps, because mailboxes get created and the DNS is assumed.
When something changes: a seed test at each major provider. This is the check to run when reply rates fall on one domain and not its siblings, because it separates a filtering problem from an audience problem.
- Yes: You know which sending IPs you control, if any
- Yes: Postmaster Tools is set up for every sending domain
- Yes: Bounce and complaint rates are read per domain
- Yes: Blocklist checks run on a schedule, not on suspicion
- Yes: You have stopped treating an IP score as your reputation
- Depends: A seed test is available when one domain diverges
The number worth holding in your head
Google's sender guidelines advise keeping spam rates in Postmaster Tools below 0.10% and never reaching 0.30%. Convert that into people at your own volume before deciding it sounds comfortable. A domain sending 300 messages a day reaches the 0.30% ceiling on a single complaint.
That arithmetic is the entire argument for list quality over sending volume, and it is why sender reputation work is mostly list work wearing technical clothing. The full account of what builds and destroys the rating is in email domain reputation, the surfaces and their blind spots are in domain reputation checks, and the recovery path when a rating has already dropped is in how to improve domain reputation.
If you would rather have the list and the sending built so the reputation question stays boring, we will build the first campaign with you.
Provider documentation and tool positioning verified as of August 2026. Verify current terms with the provider before relying on them.
Frequently asked questions.
Frequently asked questions- How do I check my sender reputation?
- Open Google Postmaster Tools for each sending domain, which is the one free authoritative surface for Gmail. Check blocklists across every domain on a schedule. Then read your own bounce, complaint and reply rates per domain weekly, because those move before any provider rating does and they are entirely yours.
- What is the difference between sender reputation and domain reputation?
- Sender reputation is the umbrella term. Domain reputation and IP reputation are two components of it, held separately by every receiver. A domain can be in good standing while its sending IP is not, which happens constantly on shared provider infrastructure. For most B2B senders the domain is the only component they control.
- Is there a free sender reputation checker?
- Google Postmaster Tools is free and is the only one reporting a mailbox provider's actual view of your domain. Spamhaus publishes a free domain reputation check against its own data, and blocklist aggregators are free. Tools that score an arbitrary IP or address are usually answering a security question instead.
- Why does my sender reputation look bad when my emails are delivering?
- Most likely because the score describes a shared IP address used by thousands of unrelated senders, not your domain. If your bounce rate, complaint rate and reply rates are healthy per domain and Postmaster Tools shows a good rating, an unfavourable third-party IP score is somebody else's behaviour.
About the author.
Tim Carden is CMO / CTO at RevenueFlow, which builds and operates outbound revenue engines for B2B companies. Studied at McGill University.
Tim Carden · CMO / CTO
Connect on LinkedIn →Explore more.
Ready to scale your outreach?
We build GTM engines that book real meetings. See the receipts.
Related articles.
How to Improve Domain Reputation, Step by Step
Google's own advice when a rating drops is to stop sending, then resume at a slower rate. The diagnosis that makes the pause worth taking.
Domain Reputation Check: The Two Things That Phrase Means
Half the tools ranking for this check whether a domain is dangerous. The other half check whether your email reaches an inbox. They are not substitutes.
Proofpoint Spam Filter: Diagnosing Placement Without Guesswork
Two different Proofpoint systems can stop a cold email, and the remedies have nothing in common. Telling them apart takes a minute and saves a month.
Email Domain Reputation: The Architecture That Holds at Volume
Two teams send the same 3,000 emails a day. One spreads it across eight domains and is still sending six weeks later. Reputation is scored per domain.
Office 365 Spam Filter: What Actually Triggers It
The same message lands in the inbox at one Microsoft tenant and in quarantine at the next. A setting the recipient chose decides which, and the headers say so.
SMTP Server Software: What Running Your Own Actually Costs
Postfix, Exim and hMailServer are free downloads. The cost is the IP address, its history, reverse DNS, TLS, blocklist delisting and reputation from zero.