How to separate risky and safe sending domains fast?
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Your domain reputation is tanking and you need to know, fast, which domains are burning and which are still clean. Here's how to do that audit in under an hour.
Step 1: Pull reputation data from postmaster tools
Start with Gmail's Postmaster Tools. Log in, check every sending domain you own, and look at two metrics. Domain Reputation should be "High" or "Medium" to be considered safe. Anything at "Low" or "Bad" is affected. Spam Rate should sit below 0.08%. If it's above 0.3%, that domain needs to be pulled from active sending immediately.
For Microsoft, register for the Outlook Smart Network Data Services (SNDS) program. This gives you complaint and trap-hit data per IP, which pairs with your domain-level picture from Gmail.
Step 2: Check every domain and IP against blocklists
Run each sending domain and IP through Spamhaus and Barracuda lookups. You can also use our free blocklist checker to do this quickly. A single Spamhaus SBL or PBL listing is enough to classify an asset as affected. Don't wait to see if it clears on its own.
Step 3: Review bounce data by sending source
Pull bounce logs from your ESP, broken down by sending domain or IP. A hard bounce rate above 2% is a red flag. Soft bounces that are consistently coming from the same domain, especially "mailbox full" responses at scale, can signal your mail is being deferred or rejected before it even reaches the inbox.
You're looking for patterns, not one-off failures. One bounced address isn't a signal. Twenty bounces from the same sending domain in the same hour is.
Step 4: Categorize each asset clearly
After the checks above, put each domain and IP into one of two buckets.
- Affected: domain reputation at Low or Bad in Postmaster Tools, spam rate above 0.3%, blocklisted on Spamhaus or Barracuda, or hard bounce rate above 2%.
- Safe: domain reputation at High or Medium, spam rate below 0.08%, no active blocklist listings, bounce rate under 1%.
If a domain sits in the middle (Medium reputation, no listings, bounce rate creeping toward 1.5%), flag it as "at risk" and watch it closely. Don't send high-stakes traffic through it until it stabilizes.
Step 5: Move critical traffic to safe infrastructure now
Before you do anything else with the affected domains, decide which transactional emails must keep going and route those through your safest domain immediately. Update your DNS and authentication records to reflect the new sending source. Then send a small test batch before flipping the full volume over.
And once critical traffic is safe, stop or severely limit sending from the affected domains. The goal is to prevent your clean infrastructure from inheriting a bad reputation by association.
If this audit is surfacing problems you're not sure how to fix, our SOS hotline is free and we can walk through your specific setup with you.
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