It’s possible that your email server is rejecting incoming emails for a number of reasons. Here’s a list of suggested troubleshooting steps:

1. Check server settings: Verify that your server setup is properly configured.
2. Verify network connection: Make sure your system is properly connected to the internet.
3. Check whitelist settings: Review your whitelist and make sure no accounts are being blocked.
4. Review server logs: Be sure to review your server logs for any pertinent information.