Sender Reputation: Check, Build and Fix

What is sender reputation?

Sender reputation is the running judgement a receiving mail server makes about whether people want mail from you. It isn't one global number. Gmail, Microsoft and Yahoo each keep their own view. They build it from what their users do with your mail and from outside data like DNS blocklists. When a message arrives, the receiving server weighs your reputation alongside authentication results and content. The message then goes to the inbox or the spam folder, or it's deferred or rejected outright. You don't make that call. The receiving server does.

Reputation is tied to two identifiers. IP reputation belongs to the server address your mail leaves from. If you send through an email service provider's shared pool, other senders' behaviour shapes it too. Domain reputation belongs to the domain in your From address and in your DKIM signature. It follows that domain wherever you send from. If you run cold outreach through your own Brevo account and your own sending domain, the domain is the asset you control directly. That's why authentication matters so much. Once DKIM is signed with your domain and aligned under DMARC, providers can credit the reputation to you rather than to the platform.

What signals build or damage sender reputation?

Providers don't publish their formulas. Still, public tools and provider guidelines all name the same inputs, and each one tends to go wrong in a typical way:

• Authentication. SPF, DKIM and DMARC have to pass and align with the From domain. If they fail, providers can't tie the mail to you. Good behaviour then builds nothing, and the mail is treated as unverified.
• Spam complaints. Every 'report spam' click counts directly against you. Google's sender guidelines for bulk senders set a maximum spam rate, and Postmaster Tools shows you where your domain stands against it.
• Hard bounces. Permanent 'user unknown' rejections for addresses that don't exist tell providers your list is old or guessed. Scraped and pattern-guessed lists are the usual cause.
• Spam traps. These are addresses that never sign up for anything, or long-dead addresses that have been recycled. Hitting one shows you sent without consent or without cleaning your list.
• Blocklist listings. Receiving servers query Spamhaus and other DNS blocklists in real time. One listing can trigger rejections at many providers at once.
• Volume pattern. A sudden spike from a domain that was quiet looks like a hijacked account or a new spammer. Steady, gradual volume doesn't.
• Recipient behaviour. Replies, mail moved out of spam and deletions without reading all count as signals. Opens are an unreliable stand-in for them.

Open rates are a particularly weak way to read reputation, because privacy features distort them. Our piece on what cold senders can trust about open rate tracking explains why.

Sender reputation check: which tools show what

No single sender reputation check shows you everything. Each tool sees one identifier (IP or domain) and one slice of the traffic. Comparing them on the same points shows which one answers your question:

Tool	What it rates	Who can see the data	Where it stops
Google Postmaster Tools	Your domain's mail to Gmail users: spam rate and authentication results	Only the domain owner, after verifying the domain with a DNS TXT record	Covers Gmail traffic only. It shows no data until you send a meaningful daily volume to Gmail
Microsoft SNDS	Mail from specific IP addresses to Outlook.com and Hotmail	Only whoever controls the IP range	Not usable if you send from your provider's shared IPs
Sender Score (Validity)	Outgoing mail server IPs on a 0-100 scale (per the HubSpot and Twilio pages in the search results)	Anyone can look up an IP	IP only. It says nothing about your domain if you're on a shared pool
Spamhaus domain reputation check	Domain reputation, with an explanation of how its Reputation Score is calculated (per spamhaus.org)	Public lookup	Reflects Spamhaus's own data. Other providers weigh other signals
senderreputation.org	SPF, DKIM, DMARC, blocklists and DNS in one scan, no signup (per its own page)	Public lookup	A configuration and listing scan, not a provider's view of how recipients respond

In practice, Postmaster Tools and the Spamhaus lookup tell you the most about your own domain. Sender Score and SNDS only become useful once the IP is yours. Run the configuration scan first, because a broken DKIM record makes every other result meaningless.

Is your sender reputation score public?

Part of it is. Blocklist status is public by design. Spamhaus and other DNS blocklists answer a DNS query from anyone, and that's exactly how receiving servers use them. Sender Score lookups by IP and the Spamhaus domain check are also open to anyone. What providers do internally isn't public. Gmail only shows you its view of your domain through Postmaster Tools, after you prove ownership via DNS. Microsoft's SNDS is restricted to whoever controls the IP. And no mailbox provider publishes the reputation it actually uses to filter your mail as a number. Any 'free score' site gives you its own estimate, not Gmail's or Outlook's verdict.

How to build sender reputation on a new domain

A new domain has no history, and providers treat that with caution, not trust. Building sender reputation means giving them a consistent track record they can verify:

1. 1 Publish SPF, DKIM and DMARC before the first send. Keep SPF to a single record within the SPF standard's DNS-lookup limit, and sign DKIM with your own domain, not the provider's.
2. 2 Start DMARC at p=none. You get aggregate reports without blocking your own mail. Tighten the policy once the reports show SPF and DKIM aligning.
3. 3 Register the domain in Google Postmaster Tools at the start, so data begins building as soon as your volume allows.
4. 4 Ramp up volume gradually and keep it steady from day to day. Avoid large batches followed by silence.
5. 5 Verify the list before importing it, and remove every address that hard-bounces on the first attempt.
6. 6 Include a working unsubscribe option and act on every request. An unsubscribe costs you nothing, while a spam complaint counts against you.

Our guide to DKIM, DMARC and SPF for cold email senders goes through the DNS side record by record. If your domain is hosted at GoDaddy, the GoDaddy DKIM setup for Brevo covers the Host-field quirk. Our email warm-up guide with daily volumes covers the volume ramp itself.

How do I fix my sender reputation?

Find the cause first, then cut your volume while the signals recover. Repair is slow because providers judge your recent behaviour over time. Work through it in this order:

1. 1 Check authentication. If DKIM or SPF started failing after a DNS change, fix that first. Nothing else counts until authentication passes.
2. 2 Look up blocklists. If you're listed, remove whatever caused the listing first. Then follow the delisting process on that blocklist's own site.
3. 3 Read the bounce messages. A wave of 'user unknown' rejections points to the list. Rejections that cite policy or authentication point to your setup.
4. 4 Stop sending to the segment that caused the problem, and lower your daily volume.
5. 5 Resume with your most recently verified contacts. Then add older segments back slowly.

Two things don't work. One is switching to a fresh domain while keeping the same list and the same copy. The new domain starts with no history and picks up the same complaints. The other is paying for delisting from a blocklist run by an independent organisation. If you're reading SMTP errors during a repair, our breakdown of email bounce codes and their causes explains what each code means.

How EmailFlow OS handles the sender side

EmailFlow OS is built so your reputation stays with you, not with a platform. You record one video and upload it. You connect your own Brevo account and your own sending domain, then import your prospect list into EmailFlow OS. EmailFlow OS creates a personalised version of that single recording for each recipient (per person, not per company). It sends each version from your own inbox, through your Brevo account and your domain, and never through a shared platform sender. So the authentication records you publish and the reputation you build stay tied to your domain, and you can watch them with the tools above. EmailFlow OS controls what gets sent and from which domain. Each receiving server still decides how to filter each message. The EmailFlow OS personalised video email page shows how this fits into outreach.

Questions people ask

? What is the difference between IP reputation and domain reputation?

IP reputation is attached to the server address that sends your mail, and on a shared provider pool you share it with other senders. Domain reputation is attached to your From and DKIM domain and stays with you if you change providers. On shared IPs, domain reputation is the part your own behaviour controls.

? How long does it take to repair sender reputation?

No provider publishes a duration. Providers weigh your recent sending history, so you recover only after complaints, bounces and blocklist listings stop and you've sent clean, steady volume for a while. A blocklist delisting can come through quickly once the cause is gone. Reputation at Gmail or Outlook recovers more gradually.

? Does a new domain start with good sender reputation?

No. A new domain has no history, and providers treat that as unknown, not trusted. That's why receiving servers often filter sudden high volume from a fresh domain to spam or defer it. Authenticated DNS records and a gradual, steady volume ramp give providers a track record to judge.