# Unknown User

*Email Deliverability*. The removal of recipient email address that doesn't exist on the recipient email server from a contact list.

This error displays as `Bounced - Unknown User`. It indicates the email address doesn't exist and you receive `Unknown User` response.

## Additional entries

* [Bounces](/docs/glossary/bounces/)
* [Subscriber List Management](/docs/glossary/subscriber-list-management/)