The RMail server sends Proof Records in the form of Acknowledgment emails back to the sender shortly after a Registered Email is sent. This Acknowledgment email confirms the processing of the message.  If you do not wish to receive these acknowledgments, the feature may be disabled in the settings as shown in the screenshots below.

1. Click on File

2. Go to RMail Settings

3. Select Track & Prove from the Settings options and in Proof Records, uncheck the box Receive Acknowledgment emails confirming processing of message

4. Click on Apply