How do ESPs enforce bounce thresholds?

You send a campaign, and a few hours later your ESP sends you a warning email. Your bounce rate crossed a threshold. Now what? And how far does it go before they pull the plug on your account?

ESPs enforce bounce thresholds for a reason that's easy to miss when you're panicking about your own account. On a shared IP, every sender's reputation bleeds into everyone else's. If your bad list drags down the IP's standing with Gmail or Outlook, senders next to you on that IP suffer too. ESPs aren't being harsh. They're protecting the whole ecosystem.

The enforcement typically follows a staged escalation, though the exact numbers vary by platform. Here's the rough pattern most ESPs follow:

• Around 2% hard bounces: You get a warning. This is informational, not punitive. But it's a real signal. Don't ignore it.
• Around 5% hard bounces: Your account gets flagged. Sending may continue but with tighter volume limits applied automatically. Some ESPs require you to acknowledge the issue before your next send.
• Around 10% hard bounces: Sending is suspended. Not throttled. Suspended. You'll typically need to submit a written explanation of what caused the spike and show a clear plan to fix it.

It's worth knowing that hard bounces and soft bounces are counted differently. Soft bounces (temporary delivery failures) get more grace. Hard bounces (permanent failures, like an address that doesn't exist) hit the threshold fast because they're a direct indicator of list quality problems.

If you're already flagged or suspended, the remediation path usually looks like this:

1. Explain the spike honestly. Was it an old imported list? A purchased list? (Buying lists is how you end up here, by the way.) A broken signup form? ESPs have seen every scenario. Be straight with them.
2. Show your hygiene plan. This means removing the invalid addresses, running a validation pass on the rest of the list, and suppressing all hard-bounced addresses permanently. Some ESPs require proof before they'll lift a restriction.
3. Demonstrate improvement before your next send. Sending again immediately after a suspension with the same list is the fastest way to get your account closed permanently.

The suppression list part matters more than people realise. Once an address hard bounces, it should never receive another email from you. ESPs track whether you're re-sending to known bad addresses, and doing that is treated as a sign that you're either careless or acting in bad faith. Suppression lists exist specifically to prevent this.

If your list feels stale or you're not sure what's in it, getting it cleaned before you hit a threshold is much easier than trying to recover after a suspension. We do that (hi ;)). You can find out more at RME Clean. Or if your account is already suspended and you're not sure what to say to your ESP, our SOS hotline is free and we'll help you figure out what to write.