Bounce rate and suppression

A bounce is a rejection by the receiving mail server. It is the clearest signal you get about list quality, and it is the number that decides whether your mail keeps arriving: mailbox providers watch bounce rates to judge whether a sender is careless, and a careless sender gets filtered long before anyone tells them.

Your bounce rate is bounces divided by everything you sent in the window.

Where you see it

Overview shows it three ways: as one of the four measures, as the red segment under Delivered volume, and per domain in the Sending domains table.

A bounce is not a failure. The two are counted separately and never overlap. A bounce means a receiving server took the message and rejected it. A failure means the message stopped before that: a malformed address, a send that was cancelled, a downstream problem. Both stop the mail; only one tells you something about your list.

The thresholds

Epostix flags a domain at two levels.

Bounce rate	What happens
Under 2%	Nothing. This is normal.
2% or higher	The domain is marked Bounce rate high and the figure turns amber
5% or higher	The domain is marked Bouncing heavily, the figure turns red, and it is raised in the attention band at the top of Overview

These thresholds are per domain, not per workspace. One bad domain is flagged on its own even when your overall rate looks healthy. That is the point, because reputation is tracked per domain.

Hard, soft, and infrastructure

Not every bounce means the same thing.

Kind	Meaning	Example
Hard	The address does not exist and will not start existing	Unknown mailbox, bad destination domain, account disabled
Soft	The address exists but could not take the message now	Mailbox full, message too large, mailing-list expansion problem
Infrastructure	The rejection was about policy or transport, not the recipient	Encryption required, authentication rejected, message integrity failure

Hard bounces are the ones that damage reputation. A high hard-bounce rate says you are mailing addresses you never confirmed.

What Epostix does automatically

You do not have to prune your list by hand. Bounces suppress addresses on their own.

A hard bounce suppresses the address permanently, on the first occurrence. There is no tolerance here, because a second attempt at an address that does not exist is the exact behaviour providers penalise. The record is kept for 180 days.

A soft bounce is tolerated, then escalates. Three soft bounces in a row, with no more than fourteen days between consecutive ones, suppress the address for fourteen days. Three more after that suppress it again. After that, one further soft bounce makes the suppression permanent. A soft bounce record is kept for seven days.

While an address is temporarily suppressed it cannot escalate further, so a single bad week does not push a recoverable address to permanent.

note

Suppression is per address, not per campaign. Once an address is suppressed, nothing you send reaches it until the suppression lifts, including transactional mail.

When the rate is high

Work down this list in order.

1. Check which domain. The Sending domains table attributes bounces per domain. A workspace-wide rate hides the fact that one domain is usually responsible.
2. Check what changed. The Delivered volume chart shows bounces per day. A rate that jumped on one day is a bad import or a single campaign; a rate that climbed steadily is list decay.
3. Check the domain is still authenticated. A domain whose SPF or DKIM record has stopped resolving will bounce at providers that reject unauthenticated mail. Its DNS health panel says so directly.
4. Stop sending to unconfirmed addresses. Purchased, scraped, or years-old lists are the usual cause. Nothing in the platform can repair a list that was never opt-in.

Bounce rate responds slowly. Once providers have judged a domain, cleaning the list stops the damage but does not immediately undo it. Recovery is measured in weeks of clean sending, which is the strongest argument for keeping the rate low while it already is.