How to check your domain reputation before sending cold emails

The health check you should run before every campaign

Most sales teams check their email copy before sending. Far fewer check their domain reputation. That's a costly oversight.

Your domain reputation is the trust score that inbox providers assign to your sending domain based on your entire email history. It determines whether your emails land in the primary inbox, the spam folder, or get blocked entirely — regardless of how good your subject line is.

Checking domain reputation before launching a campaign takes less than ten minutes. Finding out mid-campaign that your domain is flagged or blacklisted costs you every email you've sent to prospects who never saw them. The asymmetry makes the check non-negotiable. Here's exactly how to do it.

What domain reputation actually measures

Inbox providers evaluate your sending domain on several dimensions simultaneously:

• Sending history — how long and consistently your domain has been sending
• Engagement signals — open rates, reply rates, and spam-to-inbox moves from your warmup and campaigns
• Complaint rate — how often recipients mark your emails as spam
• Bounce rate — how often your emails fail to deliver
• Authentication — whether SPF, DKIM, and DMARC are properly configured
• Blacklist status — whether your domain or IP appears on known spam blocklists

Google Postmaster Tools rates domain reputation on a four-point scale: High, Medium, Low, and Bad. High reputation means Gmail trusts your domain and your emails will rarely be marked as spam. Bad reputation means Gmail is automatically sending a significant portion of your messages to spam regardless of content.

Tool 1: Google Postmaster Tools (free — essential)

Google Postmaster Tools is a free service from Google that gives you direct visibility into how Gmail evaluates your sending domain. Since Gmail handles over 1.8 billion email accounts globally, a High rating here is the clearest signal that your cold email infrastructure is healthy.

What it shows

• Domain reputation — High, Medium, Low, or Bad, updated daily
• IP reputation — how Gmail views the sending IP addresses you use
• Spam rate — the percentage of your emails that Gmail users mark as spam (target: below 0.1%; danger zone: above 0.3%)
• Authentication — the rate at which your emails pass SPF, DKIM, and DMARC checks
• Delivery errors — technical errors that prevent delivery

How to set it up

1. Go to postmaster.google.com and sign in with a Google account.
2. Click the + button to add your sending domain (e.g. yoursenddomain.com).
3. Verify domain ownership by adding a DNS TXT record provided by Google (typically takes 15 to 30 minutes to propagate).
4. Once verified, data begins populating after you've sent enough email to Gmail addresses. You need to send at least 100 emails per day to Gmail addresses before dashboard metrics appear.

Note: Google retired the V1 interface in September 2025. All users are now on V2, which includes an updated compliance dashboard and new reporting.

What to look for

Check the Domain Reputation dashboard first. Any rating below High warrants investigation before launching campaigns. If you see Low or Bad, pause sending and diagnose the cause — it could be authentication issues, high spam complaint rates, or bounce problems.

Check Spam Rate next. Keep it below 0.1%. If you're above 0.3%, you're in dangerous territory and should immediately review your list quality, unsubscribe mechanism, and email content.

Tool 2: Microsoft SNDS (free — essential for Outlook)

Microsoft's Smart Network Data Services (SNDS) provides reputation data for IP addresses sending to Outlook, Hotmail, and Live email accounts. Since Microsoft now enforces bulk sender requirements (from May 2025), monitoring your reputation with Microsoft is as important as monitoring with Google.

SNDS uses a color-coded system: green (clean), yellow (some issues), red (significant problems). Register your sending IPs at postmaster.live.com to access SNDS data.

Tool 3: MXToolbox blacklist check (free — comprehensive)

MXToolbox's blacklist checker simultaneously checks your domain and IP address against more than 100 known email blacklists (also called blocklists or DNSBLs). A domain or IP on a major blacklist — Spamhaus, Barracuda, SORBS — will see significant deliverability problems with any inbox provider that consults that blacklist.

Run your blacklist check at mxtoolbox.com/blacklists.aspx. If your domain or IP appears on any major list, the tool shows which list and typically provides a delisting request link. Delisting usually requires resolving the underlying behavior that caused the listing and submitting a manual review request.

Run this check before every campaign launch and any time you see sudden deliverability drops.

Tool 4: Mail-Tester (free — pre-send check)

Mail-Tester provides an all-in-one deliverability score by analyzing an actual test email you send to a unique address they generate. The score (out of 10) reflects authentication setup, domain reputation, content quality, blacklist status, and other deliverability factors in one place.

Send a test email exactly as you plan to send your actual campaign, then check the score. Aim for 9/10 or higher before launching any campaign. The tool identifies specific issues and their relative impact, giving you a prioritized fix list.

Tool 5: Validity Sender Score (free — IP reputation)

Sender Score, maintained by Validity, provides a 0 to 100 score for your sending IP address based on data from more than 80 mailbox and message security providers globally. A score of 90 or above indicates a strong reputation. Below 70 suggests problems that are affecting deliverability.

Note that Sender Score measures IP reputation, not domain reputation. For cold email sent through Google Workspace or Microsoft 365, the IP is typically shared infrastructure — your domain reputation (from Postmaster Tools) is the more relevant signal.

Pre-campaign domain health checklist

Check	Tool	Pass threshold	Frequency
Domain reputation	Google Postmaster Tools	High or Medium	Before each campaign
Spam complaint rate	Google Postmaster Tools	Below 0.1%	Weekly during campaigns
Blacklist status	MXToolbox Blacklist Check	Not listed on any major list	Before each campaign
Authentication pass rate	Google Postmaster Tools	100% (or near)	Before each campaign
Overall deliverability score	Mail-Tester	9/10 or higher	Before each campaign
Microsoft reputation	Microsoft SNDS	Green	Before each campaign

What to do when reputation is Low or Bad

Do not try to send your way out of a reputation drop. Sending more email when reputation is Low or Bad makes it worse, as every additional complaint or bounce compounds the signal.

The recovery process:

1. Stop cold sends immediately.
2. Diagnose the cause — check your authentication records, review your recent bounce rates and complaint rates, inspect your list for stale or unverified addresses.
3. Fix the underlying problem.
4. Resume sending at very low volume (10 to 20 emails per day) with your cleanest, most engaged contacts to rebuild positive engagement signals.
5. Monitor daily until reputation returns to High or Medium before scaling again.

Recovery from Low reputation typically takes 2 to 4 weeks of clean sending. Recovery from Bad reputation can take 4 to 8 weeks or longer. Prevention through regular monitoring is far less costly.

References

• ActiveCampaign Help Center. Check Your Domain Reputation with Google Postmaster (March 2026)
• Google Gmail Help. Postmaster Tools Dashboards
• Google Workspace Admin Help. Set up Postmaster Tools
• TrulyInbox. Google Postmaster Tools: All You Need to Know (2026) (March 2026)
• Mailtrap. Google Postmaster Tools: Tutorial 2026 (April 2026)
• Mailgun. Google Postmaster Tools: Understanding Sender Reputation (December 2025)
• SocketLabs. Google Postmaster Tools: Guide to Check Your Domain Reputation (August 2024)
• DirectMail. Keep Tabs on Your Gmail Reputation With Google Postmaster Tools (July 2025)
• Mailforge. How to Monitor IP Reputation with Google Postmaster Tools

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Mailflo monitors domain reputation, authentication health, and blacklist status for every sending domain in your infrastructure — so problems are caught before they affect your campaigns.