High bounce rate

Updated Mar 26, 2026 · 4 min read

When bounces spike, the cause is almost always list quality.

On this page · 2

Diagnose
Fix

A sudden bounce-rate spike is the fastest way to lose sender reputation. Above 4% sustained, mailbox providers start aggressive filtering. Above 8%, Inboxlee auto-suspends.

Diagnose

Open the mailbox page → Bounces tab. Sort by bounce reason. Three patterns to look for:

Mostly "user unknown" - list-quality problem. Run the list through ZeroBounce.

Mostly "domain not found" - your list contains expired or fake domains. Re-validate.

Mostly "rate limited" - you exceeded the recipient mail server's tolerance. Slow down.

Fix

Pause sending. Clean the list. Resume at half volume and ramp back over a week. Suppress any address that hard-bounces - never retry.

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