Email bounce rate: measure the cause

Email bounce rate is the proportion of attempted messages a sending system reports as undeliverable over a defined period. It describes real sending outcomes, not verification status. Use a consistent denominator, distinguish persistent and temporary failures, and investigate reasons before assuming every bounce represents an invalid email address.

Last updated 2026-09-14. Read the scope and limitations before applying a result.

Key points

Define the denominator.
Separate temporary and persistent failures.
Verification cannot predict every bounce.

Detailed explanation

Retain response details, time periods, and campaign context. Sender-related decisions and receiving policies can also prevent delivery. Compare like-for-like campaigns.

Example

100 undeliverable messages out of 5,000 attempted sends is 2%.

How RefreshList handles it

The bounce calculator estimates an assumed rate, not guaranteed savings or delivery.

Limitations

No universal safe threshold or guaranteed reduction is asserted. Follow the sending provider’s actual rules.

Methodology and sources

Product behavior is described from the current RefreshList implementation and provider contract. Protocol context should be checked against the applicable standards and provider documentation. This page does not create a benchmark or certification.