You are viewing the email acknowledgement report for an online form such as a donation or event registration form under Email > Acknowledgements. The status may say failed with no acknowledgements sent. When you send a test message from your NetCommunity site under Email > Messages, you may see the following error returned as an exception:
ExceptionOnServer: Bad Request: Unable to automatically map user (blackbaudhost\59650user) to a valid organization/application.
If your NetCommunity site is hosted by Blackbaud, contact support and reference this article.
If you host your NetCommunity server locally, verify the Blackbaud Service credentials are entered correctly on the site under Administration > Sites & Settings > Web services tab. Recycle application pools.