How do you confirm reputation is the root cause?

Your open rates have tanked, more mail is landing in spam, and you're pretty sure your sender reputation is the culprit. But before you start making changes, you want to be sure. Reputation problems look similar to technical failures on the surface, so the goal here is to rule things out one by one.

Here's how to actually confirm reputation is the root cause.

Step 1: Check your authentication is passing

Start here because a broken authentication setup can cause the exact same symptoms as a reputation problem. Send yourself a test email and pull the full headers. You're looking for SPF, DKIM, and DMARC to all show "pass." If any of them are failing, that's your root cause and you don't need to go further. You can also run a quick check with our free SPF checker or DKIM lookup.

Step 2: Check Gmail Postmaster Tools

Gmail Postmaster Tools gives you a direct reputation signal from the provider that handles around half of consumer inboxes. Log in and look at two things specifically. First, the Domain Reputation chart. You want to see "High" (green). If it shows "Medium," "Low," or "Bad," that's a clear confirmation of a reputation issue. Second, the Spam Rate chart. If your spam rate is above 0.10%, that's a warning. Above 0.30% is serious. A spike that matches the timing of your deliverability drop is strong evidence.

Step 3: Check Microsoft SNDS

Microsoft's Smart Network Data Services (SNDS) gives you IP-level reputation data for Outlook and Hotmail. Look for your sending IP's status. Green means healthy. Yellow is a caution. Red means Microsoft is actively filtering or blocking your mail. If you're on a shared IP through your ESP, ask them for the IP address first, then check it here.

Step 4: Run a blocklist check

Some deliverability problems aren't about soft reputation signals at all. They're caused by your domain or IP appearing on a blocklist. Check both your sending domain and your sending IP. Spamhaus is the most impactful list to check. A listing there causes widespread filtering across nearly every major provider. You can also check multiple lists at once using our free blocklist checker.

Step 5: Analyze your bounce messages

Your bounce messages will usually tell you exactly what's happening if you know what to read. Reputation-related rejections look different from technical ones. Phrases like "Your message was detected as spam," "550 5.7.1 blocked," or references to a blocklist name all point to reputation. Technical failures usually say things like "connection timeout" or "DNS lookup failed." If your bounces are citing content or policy violations, that's a different problem again. Pull the last 50 hard bounces from your ESP and look at the message text directly.

Step 6: Compare across providers

Still this is the diagnostic step that most people skip, and it's genuinely revealing. Pull your delivery and inbox placement rates broken down by recipient domain. If your mail is going to spam at Gmail but delivering fine at Yahoo, the problem is likely Gmail-specific. If it's bad everywhere, the issue is almost certainly your domain reputation or a major blocklist hit. If it's fine everywhere except one corporate domain, that's a local filtering rule on their end, not your reputation at all.

Once you've gone through these six checks, you'll have a clear picture. Authentication passing but reputation scores low? Reputation is the root cause. Authentication failing? Fix that first. On a major blocklist? That's where to start. The first step in reputation repair is much easier once you know exactly what you're dealing with.

If you've run through all of this and still can't pinpoint the cause, our SOS hotline is free. Sometimes a second pair of eyes on your headers and bounce logs is all it takes.