Out: 452 4.3.1 Insufficient system storage

The key line in the log is:

452 4.3.1 Insufficient system storage

What It Means:

452 4.3.1 Insufficient system storage
This indicates that the server is temporarily unable to accept the message due to insufficient system resources, most commonly a lack of available disk space.

Step-by-Step Explanation of the Session:

• ehlo localhost.localdomain: The remote server introduces itself.

• mail FROM:<[email protected]> size=507: The sender address is provided.

• 452 4.3.1 Insufficient system storage: Your server rejects the message because it lacks sufficient resources to accept it.

• rset: The session is reset.

• quit: The session is closed.

What You Should Do:

1. Check Disk Space:

df -h

Pay special attention to the /, /var, or /var/spool partitions.

2. Check the Mail Queue (optional):

mailq

3. Clean Up Unnecessary Files:

   • Large log files (/var/log)

   • Postfix mail queue files (/var/spool/postfix)

   • Temporary files (/tmp)

4. Restart Postfix After Cleanup:

systemctl restart postfix

Summary:

Your Postfix server rejected an incoming message because there wasn’t enough system storage (likely disk space). Clean up the disk, free up space, and then restart Postfix.

If you'd like, I can help analyze your current disk usage — just share the output of the following commands:

df -h
du -sh /var/*

Let me know if you need help with any step.