How to identify false bounces from filters or blocklists?
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A false bounce is a rejection where the address is real and deliverable, but your message was blocked for reasons unrelated to the address itself. Spam filters and blocklists generate these regularly, and if you suppress the address without investigating the cause, you'll suppress valid subscribers while the actual problem (your reputation or content) continues untreated.
Here's how to tell a false bounce from a genuine one:
Check the bounce code and message text. Real hard bounces (invalid address, nonexistent mailbox) return codes like 550 5.1.1 with language about the user or mailbox not existing. False bounces from filters return codes like 550 5.7.1 or 554 5.7.0 with language about spam, policy, or reputation. The difference is in the error text. "User unknown" is a real hard bounce. "Message rejected due to content policy" is a false bounce.
Look for patterns by domain or provider. If you're seeing rejections from one specific domain (say, all @bigcorp.com addresses bouncing) but not others, that's almost certainly a filter or blocklist issue, not invalid addresses. If the same addresses delivered fine last week, they're not suddenly invalid.
Check whether you're blocklisted. Run your sending domain and IP through a blocklist checker. Our free blocklist checker covers the major lists. If you're listed on Spamhaus or another major list, that explains rejections across multiple recipients without any problem with the addresses themselves.
Test a known-valid address at the same domain. Send a test email to an address at the same domain that you know is valid (your own domain, a colleague's, a test account). If that also fails with a policy message, the issue is your sending domain's reputation with that receiver, not the specific address that bounced.
The right response to a confirmed false bounce: don't suppress the address. Instead, fix the underlying reputation or content issue first. Then resend to the affected addresses once delivery is working again. If you suppress them, you lose real subscribers who wanted to hear from you.
Need help diagnosing a specific pattern? Talk to us and we'll help you distinguish real bounces from reputation problems.
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