Bounces and auto-pause

We auto-pause sending from an inbox that's bouncing too much, to protect your domain reputation.

How it works

• Every time an inbox sends, we increment its send count.
• Every time an inbound message is classified as a bounce (DSN subject, mailer-daemon sender, etc.) we increment the bounce count.
• If the bounce rate over a recent window crosses our threshold, we set the inbox to paused.
• A paused inbox returns 403 INBOX_PAUSED on any send attempt. Inbound still works.

Why pause instead of just warn

A high bounce rate burns domain reputation fast. If we didn't pause, one agent stuck in a retry loop against a bad address could mark your whole sending domain as spam to Gmail and Outlook. Pausing is aggressive but it protects your deliverability.

Unpausing

Currently, unpausing is manual — contact support. Usually we want to understand what caused the bounce burst before unpausing, so we can help you avoid it next time. A planned future feature is a self-service unpause endpoint with a cooldown.

Avoiding the problem

• Always validate recipient addresses before sending. Use POST /v1/verify-email as the pre-flight MX check, then pass verified: true on the send.
• Don't retry on a permanent bounce. If a send fails with a 5xx from the relay, assume the address is dead and move on.
• Watch GET /v1/metrics — it exposes sent, received, and bounced counts you can alert on.