When emails bounce back and you're experiencing issues with CageFS and proxyexecd, it may be due to a conflict in configurations. Here are steps to troubleshoot and potentially resolve the issue:

1. Check CageFS Configuration:

   Make sure that CageFS is properly configured on your server. Verify that it's not causing any conflicts with the mail server.

2. Review Proxyexecd Configuration:

   Check the configuration of proxyexecd. This is a service that executes processes on behalf of users. Ensure that it's set up correctly and doesn't conflict with mail delivery.

3. Verify Exim or Postfix Configuration:

   Ensure that your mail server (Exim or Postfix) is configured to work with CageFS. It's possible that the mail server may be trying to execute a process in a way that CageFS doesn't allow.

4. Check CageFS Mount Points:

   Verify that the necessary directories for mail processing are mounted in CageFS. This includes /var/spool/exim or /var/spool/postfix directories.

5. Check User Permissions:

   Make sure that the users sending emails have the appropriate permissions to access and use the mail server. This includes permissions within CageFS.

6. Review Exim/Postfix Logs:

   Check the logs of your mail server (Exim or Postfix) for any error messages or warnings that may provide more insight into why emails are bouncing back.

7. Check for Specific Error Messages:

   Look for specific error messages in the bounce-back emails. These messages can often provide clues as to why the emails are failing to be delivered.

8. Verify DNS Settings:

   Ensure that your server's DNS settings are correctly configured. Incorrect DNS settings can lead to email delivery issues.

9. Check for Resource Limitations:

   If you're using CloudLinux or a similar system, verify that the users sending emails aren't hitting any resource limits imposed by CageFS.

10. Disable CageFS (Temporary):

    As a temporary measure for testing, you can try disabling CageFS to see if it resolves the email bouncing issue. This can help determine if CageFS is indeed the cause.

11. Contact CloudLinux Support:

    If none of the above steps resolve the issue, consider reaching out to CloudLinux support for further assistance. They may have specific recommendations or solutions for CageFS-related mail issues.

Remember to proceed with caution and always have backups available before making significant modifications to your server configuration.