What are the main indicators of reputation collapse?

Your open rates just fell off a cliff. Complaints are ticking up. Something feels wrong, but you're not sure if this is a bad week or the start of something serious. Here's how to tell the difference.

Reputation collapse doesn't usually announce itself all at once. It tends to show up across multiple signals at the same time, and that clustering is the key diagnostic clue. One bad metric is a blip. Three bad metrics in the same send window is a pattern worth taking seriously.

These are the main indicators to watch:

• Open rate crash. A drop of 50% or more across consecutive campaigns, especially when it's concentrated at one provider like Gmail or Outlook. Provider-specific drops usually mean a reputation issue at that inbox, not a content problem.
• Complaint rate above 0.3%. Google's threshold for action is 0.1% and 0.3% is the danger zone. If you're hitting or passing that number, filtering is almost certainly already happening. The complaints you see are always an undercount of the real figure.
• Gmail Postmaster Tools showing Low or Bad. This is one of the clearest signals available. Gmail's domain reputation rating going from Medium to Low (or worse, to Bad) means Gmail has already started routing your mail differently. You can check this inside Gmail Postmaster Tools if you've set it up.
• New bounce types appearing. Especially policy-based blocks like 550 5.7.1 or messages referencing authentication failures or sender reputation. These are different from the soft bounces of a normal send. They mean a receiving server is actively refusing your mail.
• Blocklist presence. Appearing on a major list like Spamhaus is a hard signal. It doesn't cause reputation collapse on its own, but it's often a symptom of the same underlying behavior that caused the collapse. You can run a free check at our blocklist checker.
• Engagement collapse beyond opens. Clicks disappear. Replies stop. If people who used to engage are now completely silent, the most likely explanation is that they're not seeing your email at all.
• Seed testing shows spam folder placement. If you use seed tests (or inbox placement tools), a dramatic shift toward spam folder delivery is a direct confirmation of what the other signals are suggesting.
• Throttling and deferrals increase. Receiving servers start slowing down your mail, accepting messages more slowly or temporarily rejecting them. This is often a pre-filter step before full blocking.

The timeframe matters too. Reputation collapse triggered by a single bad campaign can show up within 24 to 48 hours. Gradual decay from ongoing list hygiene issues usually takes weeks or months to become visible. Seeing these signals appear fast, after a specific send, points to an acute cause. Seeing them creep in slowly suggests a systemic degradation problem that's been building under the surface.

If you're seeing three or more of these signals together, treat it as a genuine emergency. The longer you keep sending at the same volume without diagnosing the root cause, the deeper the hole gets. Start by checking your complaint rate and Postmaster data, then look at whether the problem is domain-level or IP-level before you start fixing anything.

Not sure where to start? Our SOS hotline is free and there's no pitch attached. We'll help you figure out what's actually happening.