Domain reputation: checking Gmail, Microsoft and the blocklists

Your domain has a separate reputation at each receiver, and the receivers don't share them. Gmail keeps one. Microsoft keeps one, mostly per IP. Each blocklist keeps a yes or no. A tool that prints a single score for your domain uses a model of its own, and no mail server consults that score.

Check each receiver separately, starting with the one that handles most of your mail.

Which one should I check first? Google Postmaster Tools. It shows Gmail's own rating of your domain, and most domains have never set it up.

Google Postmaster Tools

Google shows Gmail's rating of your domain in Postmaster Tools. It's free and reports on the actual traffic between your domain and Gmail users. If you send any volume to Gmail, check it first.

1. Sign in with any Google account and add a domain. Google's instruction is to enter the domain you use to authenticate outgoing email with SPF or DKIM, or both. That's the domain in your DKIM d= tag or your return path, which may be a subdomain.
2. Verify it. Google gives you a TXT or CNAME record to add at your DNS host. Verification is usually immediate and can take up to ten minutes.
3. Open the Domain reputation dashboard. Only the original version of Postmaster Tools has it. Google has said it will retire that dashboard, and the new version shows no reputation grade.

Google rates a domain at one of four levels, described here in Google's own words:

• High: a history of very low spam rates, complying with Gmail's sender guidelines. Mail is rarely marked as spam.
• Medium: a history of legitimate email, but occasionally sends spam. Most mail has a fair deliverability rate.
• Low: a history of sending a significant volume of spam regularly. Mail is likely to be marked as spam.
• Bad: a history of sending a high volume of spam regularly. Mail is almost always marked as spam or rejected.

The Spam rate and Authentication dashboards matter too. Spam rate is the share of your delivered mail that Gmail users reported. Google's requirement, when I last checked, is to stay under 0.10% and never reach 0.30%. The sender guidelines carry the current numbers. Authentication shows what share of your traffic passed SPF, DKIM and DMARC, which is the first thing to fix when reputation is low.

Google withholds data on days when your volume to Gmail is low, to protect its users. A domain sending a few hundred messages a day to Gmail can go weeks with no data. In that case Google hasn't rated the domain at all, which is normal for a small sender.

Microsoft SNDS

Microsoft's equivalent is Smart Network Data Services, SNDS. It reports per IP address rather than per domain, so you have to own the IP. Sign in with a Microsoft account, request access to the IPs you're responsible for, and confirm through the address Microsoft mails at the network's abuse or postmaster contact.

Once in, SNDS shows each IP's filter result for the day, green, yellow or red, and its complaint rate from Outlook.com users. Microsoft has said trap-hit counts leave the data report from July 2026, so don't plan around that column.

If you send through Google Workspace, Microsoft 365 or any shared sending service, you don't own the IP and can't register it. Your provider does. For a domain-level problem at Microsoft, use the sender support form. It's the same page you use to ask for an IP to be unblocked.

Blocklists

Your IP or domain is on a blocklist or it isn't, and a receiver that consults the list refuses your mail or accepts it. Check Spamhaus and Barracuda directly, because large receivers and most mail filters use them.

Spamhaus keeps IP lists, queried as one zone called ZEN, and a domain list, the DBL. Look yourself up at check.spamhaus.org, or from a shell. The IP goes in reversed:

No answer means not listed. An answer starting 127.0.0. or 127.0.1. means listed, and the last number shows which list. Run this from your own resolver, or the query is refused. Spamhaus answers public resolvers like 8.8.8.8 with an error code instead of a result. Our Spamhaus delisting guide explains the codes and how to get off each list.

Barracuda keeps an IP list used by every Barracuda spam appliance and by anyone else who points at it:

127.0.0.2 means listed. Our Barracuda delisting guide covers the removal form.

The multi-list checkers, MXToolbox and the like, query dozens of lists at once. No large receiver uses most of those lists, and a listing on one of them changes nothing about your delivery. Read the result for Spamhaus and Barracuda and ignore the rest unless a bounce mentions one.

Cisco Talos

Talos Intelligence is the reputation behind Cisco's email security appliances. Look up your IP or domain and it gives an email reputation of Good, Neutral or Poor. Poor gets your mail throttled or refused by organizations running Cisco gear, which is many large companies and few consumer mailboxes. A dispute goes through the Talos support site linked from the result.

DMARC aggregate reports

Every dashboard above is a summary someone else made. The raw record of what receivers did with your mail is in the DMARC aggregate reports they send you daily, if you've put a reporting address in your DMARC record. Each report lists the servers that sent as your domain, whether each passed, and the disposition the receiver applied: delivered, quarantined or rejected.

That's where reputation problems show first, as a source that used to pass and now doesn't, or a server you've never heard of sending under your name. Reading a report by hand shows the rows. Our weekly digest reads every report that arrives and lists each sender and its result, and on a paid plan we email you the day an unfamiliar sender first fails. Your first domain is free.

What affects a reputation

Every receiver weighs the same few things, in roughly this order.

• Spam reports. Users clicking the spam button. Nothing else counts as much. Send only to people who asked, and make unsubscribing one click.
• Authentication. SPF or DKIM passing and aligned with your From domain, and a DMARC record. Failing this makes every other signal worse. Our DMARC setup guide gives the order to do it in.
• Bounces. Sending to addresses that don't exist, repeatedly, looks like a bought list.
• Spam traps. Addresses that never signed up for anything. Mail to them counts against you like bounces do, and it gets you listed faster.
• Volume swings. A domain that sends fifty a day and then fifty thousand looks like a compromised account, because it usually is.

A reputation recovers with weeks of clean traffic after you fix the cause. There's no form for it, at Google or anywhere. The blocklists are the exception, and the Spamhaus and Barracuda guides above cover them.