Your email sender reputation score is the primary signal mailbox providers use to decide whether your campaigns land in the inbox, the spam folder, or get blocked outright. It’s calculated from your sending domain and IP history — complaint rates, bounce rates, authentication status, and engagement patterns. Checking it takes under 10 minutes using free tools, but most senders don’t do it until they’re already in trouble.
Having worked through deliverability issues across eCommerce programs at every scale, the pattern is consistent: brands discover a reputation problem when revenue drops, not when the signal first appears. By then, recovery takes weeks. Running a proper email reputation check once per month — and understanding what you’re reading — closes that gap entirely.
If you’ve noticed open rates dropping, seen a sudden deliverability dip, or you’re simply trying to stay ahead of problems before they compound — this guide covers every tool worth using, what each one actually measures, and how to interpret what you find.
What You’re Actually Measuring
There is no universal reputation system. Each mailbox provider scores you independently from signals it observes in your mail — complaint rate above all, then bounce rate, engagement, authentication status and sending consistency. How email domain reputation is scored and protected breaks down each input and what moves it; what a sending domain is covers the layer underneath.
This post is about the other half of the problem: actually reading your current numbers, tool by tool, in about ten minutes.
The Tools That Actually Show You Your Reputation
1. Google Postmaster Tools
Google Postmaster Tools is the most important reputation tool for senders whose lists are predominantly Gmail users — which includes most eCommerce brands.
After verifying your sending domain, you get access to:
- Compliance status — pass or fail against Gmail’s bulk sender requirements. This is where to start
- Deliverability analysis — a diagnostic inside Compliance status that returns a plain-language recommendation about your domain’s standing, triggered by low volume, delivery failures, spam threshold breaches, low recipient engagement, missing opt-in signals or guideline violations
- Spam Rate — the percentage of your Gmail recipients who marked your mail as spam, as a trend over time
- Authentication — the percentage of your mail passing SPF, DKIM and DMARC
- Delivery Errors — specific error codes if Gmail is rejecting or deferring your mail
- Domain Reputation and IP Reputation — the familiar High / Medium / Low / Bad tiers
Read that last bullet as a legacy signal. Google has stated that the Domain and IP Reputation dashboards will be retired; it has not published a date, and as of August 2026 both are still there. So they still work — they just have no future, and there are no reputation endpoints in the v2 API. If you have a monthly process built on screenshotting a reputation tier, move it to Compliance status now rather than when the notice lands.
The spam rate chart remains the single most useful data point in the tool. Trending upward means an active problem; a spike on a specific date correlates to a specific campaign. What each threshold on that chart actually triggers is covered in Gmail’s spam rate thresholds.
One caveat: Postmaster Tools only shows data when you’re sending sufficient volume to Gmail, and historical data doesn’t backfill — set it up before you need it. For a full walkthrough of every dashboard, see the Google Postmaster Tools guide, or connect it to InboxEagle’s Postmaster integration to have the data pulled for you.
2. Microsoft SNDS (Smart Network Data Services)
Microsoft SNDS is Microsoft’s equivalent for Outlook, Hotmail, and Live.com recipients. It’s IP-based rather than domain-based.
After requesting access for your sending IP range, SNDS shows:
- A color-coded reputation per IP: Green (good), Yellow (neutral), Red (problematic)
- Spam complaint rates from Outlook users
- Spam trap hit counts — a direct indicator of list quality issues, and worth reading alongside what spam traps are and how you acquire them
Red status on SNDS frequently means your mail is being filtered or blocked for Outlook recipients even when Gmail delivery looks fine. Both tools are necessary because reputation is calculated independently per provider.
SNDS is also no longer the whole Microsoft story. Since May 2025, senders pushing more than 5,000 messages a day to Outlook.com, Hotmail.com or Live.com must pass SPF, DKIM and aligned DMARC or the mail is refused outright with a 550 5.7.515 error — an authentication gate that sits in front of reputation entirely. A Green SNDS score will not save mail that fails it. The Outlook bulk sender requirements cover what passing looks like. While you’re checking IPs, confirm your PTR records resolve with a reverse DNS lookup — missing or mismatched reverse DNS is its own rejection reason at both Microsoft and Gmail.
3. Barracuda Central
Barracuda Central is Barracuda Networks’ free IP reputation lookup tool. It classifies sending IPs as Good, Poor, or shows active blocklist status within the Barracuda Reputation Block List (BRBL) — one of the most widely adopted blocklists in enterprise and SMB email filtering.
Barracuda’s filtering is deployed across a large portion of business email infrastructure, particularly in mid-market and enterprise environments. A Poor classification or active BRBL listing can silently filter your mail for an entire segment of business recipients without any error codes showing up in your ESP dashboard.
The lookup is instant — enter your sending IP and you get the current reputation classification plus blocklist status in one place. If you’re experiencing unexplained filtering in business email accounts and Postmaster Tools and SNDS both look healthy, Barracuda Central is the next check to run.
4. Talos Intelligence
Talos Intelligence is Cisco’s IP and domain reputation database. It classifies sending infrastructure as Good, Neutral, or Poor.
Talos is particularly relevant because Cisco’s spam filtering is built into a significant portion of corporate email infrastructure and some ISPs. A Poor Talos classification can cause filtering that doesn’t show up in Postmaster Tools or SNDS — making it a useful cross-check when you’re experiencing unexplained deliverability issues in B2B lists or corporate email users.
5. MXToolbox
MXToolbox isn’t a reputation score tool in the same sense — it checks whether your sending domain or IP is listed on any of the major email blocklists.
Being on a blocklist is different from having poor reputation, but the two are related. If your complaint rate has been elevated for an extended period, or if you’ve sent to spam trap addresses, blocklisting often follows. Checking MXToolbox gives you a binary answer: are you on a list that would cause certain providers to reject your mail outright? Our email blacklist checker runs the same lookup, and how to check and remove an email blacklisting covers what to do with a positive result.
Why These Tools Disagree
Run all five and you will often get contradictory answers. That’s not a malfunction — it’s the most diagnostic thing the exercise produces.
Google Postmaster Tools reports on your domain. SNDS, Barracuda and Talos report on your IP. Those are two different reputations that move independently, and which one dominates depends on who you’re mailing. Gmail leans heavily on domain reputation; Microsoft weighs IP more heavily through SmartScreen; corporate filters running Cisco or Barracuda infrastructure may never look at your domain at all.
So the disagreement tells you where the damage is:
- Clean domain, dirty IP — if you’re on a shared IP, someone else’s sending caused this. You have less control and a different set of options; dedicated vs. shared IP, with data from 15,174 IPs covers when moving is actually worth it.
- Dirty domain, clean IP — this one is yours. Complaint rate, list quality, or authentication.
- Both dirty — usually a sustained complaint problem that has aged into blocklistings.
IP reputation vs. domain reputation breaks down which provider weighs which, and why the answer has been shifting toward domain for years.
How to Read the Results Together
No single tool gives you the complete picture. The correct workflow is:
- Check Google Postmaster Tools first — read Compliance status, then the spam rate. Google’s published guideline is below 0.10%; set your own alert at 0.08% so you have room to react before you’re in breach rather than after. The spam complaint rate calculator converts that into complaints-per-send for your volume.
- Cross-reference with SNDS — if Outlook delivery is failing but Gmail looks fine, you likely have a list quality issue specific to Outlook users.
- Run MXToolbox to rule out active blocklisting.
- Check Barracuda Central if you’re seeing unexplained filtering in business email accounts.
- Check Talos if you’re seeing filtering in corporate or B2B segments with Cisco infrastructure.
If all of these show healthy signals and you’re still experiencing inbox placement issues, the problem is likely engagement-based — mailbox providers are routing your mail based on recipient behavior, not hard reputation signals. That’s a segmentation and list hygiene problem, not a technical one. Our email list hygiene guide for eCommerce covers how to approach it.
What to Do When Your Email Reputation Check Comes Back Low
Finding a low reputation score is only useful if you act on it. Each signal points to a different root cause — here’s how to diagnose and fix the most common ones.
High Spam Complaint Rate
Suppress contacts who haven’t engaged in 90+ days and audit your opt-in source — importing contacts without confirmed consent keeps complaint rates elevated no matter how good the content is. What each Gmail threshold triggers covers the first 72 hours in detail.
High Bounce Rate
Clean out hard bounces and repeat soft-bouncers, then correlate the spike to the list import or segment that caused it. The bounce rate calculator gives you the current number; email list hygiene for eCommerce covers the cleanup, and validation vs. verification explains which service actually prevents the next one.
Authentication Failures
Anything below 100% on DKIM is a bug worth chasing. SPF, DKIM and DMARC explained covers what each record does; the deliverability checker tests all three against your live domain in one pass. For Klaviyo senders specifically, see email authentication in Klaviyo.
Active Blocklisting
Fix the root cause first, then request delisting. Most lists require evidence the underlying problem is resolved — complaint rate down, spam trap hits stopped — and submitting before the fix gets you re-listed quickly, which makes future removal harder. Blacklist check and removal walks the process per list.
From One-Time Check to Continuous Monitoring
The senders with consistently high inbox placement rates don’t check their reputation once and move on. They monitor it continuously — because reputation changes with every send, and a single problematic campaign can move the needle within 24 hours.
Checking these tools manually before major campaigns is a minimum floor. Automated monitoring that alerts you when signals move — complaint rate trending up, domain reputation dropping, a new blocklist entry — is what turns reputation management from reactive to proactive.
That’s what InboxEagle’s real-time deliverability monitoring is built to do: surface reputation signals automatically so you’re not running manual checks before every send. If you want a single number to start from rather than five dashboards, the email deliverability score tool grades your setup in one pass.
One closing note on where this is heading. Every reputation score in this post is a proxy — a provider’s summary of how much it trusts you. Gmail is quietly moving away from publishing that summary, and what replaces it is compliance: pass or fail, with a stated reason. That’s a better deal for senders, because “your one-click unsubscribe headers are missing” is actionable in a way that “your reputation is Medium” never was. Build your monthly check around the signals that survive that shift.
