Who Scores Your Domain Reputation, and What They Are Measuring

In part one we covered what domain reputation is: the running record of how people have responded to mail from your domain, and the thing that decides whether your campaign lands in the inbox or the junk folder.

The obvious next question is who decides. Whose opinion are we actually talking about, and what are they measuring?

There are two groups, and the distinction matters because they behave very differently.

The mailbox providers, who score you because they have to

The first group is the providers themselves. They are not scoring you as a service. They are scoring you because every message that arrives forces a decision, and reputation is how they make it at scale.

Each one keeps its own private opinion of your domain. There is no shared score. You can be in good standing with Google and in trouble with Microsoft at the same time, which is exactly the situation that produces the puzzled call about a campaign that "worked for some people".

Google weighs recipient behaviour above almost everything else. Opens, replies, deletions, and above all spam complaints. For most Australian consumer lists Gmail is the single largest slice of the audience, so its opinion carries the most weight in your overall results.

Microsoft covers Outlook, Hotmail and Microsoft 365, which makes it the one that matters most for business-to-business sending. If you are emailing Australian companies, government departments or health services, Microsoft's view of your domain is the one determining whether you reach anyone.

Yahoo, including AOL, applies broadly similar rules and enforces them on bulk senders.

Apple filters iCloud Mail more quietly than the others and publishes less about how it works, but it has been steadily tightening what it expects from bulk senders, and its share of personal addresses keeps growing.

The independent services, who score you whether you like it or not

The second group does not deliver your mail. They publish reputation data that other people consult, and their reach is much wider than most senders realise.

Spamhaus maintains blocklists used by an enormous share of the world's mail servers, including a list specifically for domains found in spam. Landing on it is not a filtering problem, it is an outright delivery problem.

Cisco Talos and Barracuda publish sender reputation that corporate security appliances rely on. If your recipients work somewhere with a proper mail gateway, and in government and enterprise they almost certainly do, these are quietly making decisions about your mail before it reaches the mailbox provider at all.

Validity Sender Score rates sending IP addresses out of 100 based on observed behaviour. It is useful mostly as an independent second opinion on how your sending looks from the outside.

The thing to understand about this second group is that their judgement feeds into the first group's decision. A poor listing does not just cost you the recipients behind that particular filter. It becomes another negative signal in the pile.

The numbers they work to

Most of this happens out of sight, but the major providers do publish the bar they expect bulk senders to clear. These are the figures worth knowing.

Your spam complaint rate must stay below 0.3 per cent. That is three complaints in every thousand emails, which sounds generous until you look at a real send. Google suggests aiming for 0.1 per cent and treating 0.3 as the ceiling rather than the target, which is the right way to think about it.

You are formally treated as a bulk sender once you are sending 5,000 or more emails a day to a single provider. Cross that line and the strict rules apply in full.

Your domain needs SPF, DKIM and DMARC all in place and aligned. This is no longer advisory. Microsoft moved through its enforcement in stages during 2025, and since late that year non-compliant bulk mail is refused outright with a permanent rejection rather than quietly filed in junk. It never reaches any folder.

Unsubscribes must be one click, no login, actioned within 48 hours.

The change that caught people out

Here is the part that trips up anyone who researched this a couple of years ago.

Google used to publish a plain domain reputation grade in Postmaster Tools: high, medium, low or bad. Senders watched it, agencies reported on it, and a lot of advice was built around checking it.

Google retired it in 2025. Their reasoning was sound, if inconvenient. A static grade lagged weeks behind what a sender was actually doing, so by the time your label dropped, the damage was already done and the number was telling you about a problem you had a fortnight ago.

What replaced it is more useful and less comfortable. Postmaster Tools now reports plain verdicts drawn from live recipient behaviour, along the lines of whether users want your mail, whether the signals are too thin to tell, or whether your spam rate has gone past the threshold. Alongside that sits a compliance view covering authentication, spam rate and unsubscribe handling.

If you go looking for your "domain reputation score" today and cannot find it, that is why. And if you find an article telling you to check it, the article is out of date.

The practical takeaway has not changed so much as sharpened. Recent behaviour is the whole game. There was never a score to earn once and keep, and now the tooling reflects that honestly.

Why we think this is good news

It is easy to read all of the above as a pile of new obstacles. We would put it the other way around.

Every one of these requirements is trivial for a business that sends wanted mail to people who asked for it, and genuinely difficult for someone buying lists and blasting them. Authentication, complaint thresholds and working unsubscribes are cheap for the legitimate sender and expensive for the other kind. The rules have been tightening for a couple of years now, and the effect has been to clear out a lot of the noise your email used to compete with.

The senders who set this up properly are landing in inboxes that are quieter than they have been in years. That is not a burden. That is an advantage, and it goes to whoever bothers.

Next in the series

Part three looks at what it actually costs when reputation slips, which is harder to spot than you would expect, because your reports keep telling you everything is fine.

If you want to see where your own domain currently stands, our inbox placement testing shows you where your mail is landing across the major providers rather than leaving you to guess from open rates.