Fix Postfix Error: Sender Address Rejected – Easy Solutions

The error message Sender address rejected: User unknown in virtual mailbox table from Postfix indicates that Postfix error is rejecting an email because it cannot find the sender’s address in the virtual mailbox table. This typically occurs when the email address of the sender is not listed in the virtual mailbox map that Postfix is using.

Here are steps to troubleshoot and fix this issue:

1. Verify Virtual Mailbox Configuration

Make sure that the virtual mailbox table is correctly configured and that it includes the sender’s address. The virtual mailbox table is usually defined in Postfix’s configuration files and can be either a database or a file.

Check the configuration:

• Open the main Postfix configuration file (/etc/postfix/main.cf):

  sudo nano /etc/postfix/main.cf

• Look for lines that specify the virtual mailbox settings. Common parameters include:

  virtual_mailbox_domains = example.com
  virtual_mailbox_maps = hash:/etc/postfix/vmailbox
  virtual_alias_maps = hash:/etc/postfix/virtual

Check the virtual mailbox file:

• If you’re using a file-based virtual mailbox map, open it (e.g., /etc/postfix/vmailbox):

  sudo nano /etc/postfix/vmailbox

• Ensure that the file contains the correct mapping for your virtual domains and users.

2. Update Virtual Mailbox Table

If you’ve made changes to the virtual mailbox map file, you need to update Postfix with the new data. If you are using a database (like MySQL or PostgreSQL), ensure the database has the correct entries.

• For file-based maps, generate the hash database file:

  sudo postmap /etc/postfix/vmailbox

• For MySQL or PostgreSQL, make sure the database table is updated correctly.

3. Check the Sender Address

Ensure that the sender address is correctly set up and included in the virtual mailbox table. If the sender address is not meant to be part of your virtual mailbox table but is still being rejected, you might need to adjust your Postfix configuration or check your sender’s email settings.

4. Review Postfix Logs

Check the Postfix log files for more detailed information about the error. The logs can provide additional context for the rejection:

• View the logs:

  sudo tail -f /var/log/mail.log

• Look for entries related to the Sender address rejected error to get more details about why the address was rejected.

5. Reload Postfix Configuration

After making changes to configuration files or mailbox maps, reload Postfix to apply the changes:

sudo systemctl reload postfix

6. Check Permissions

Ensure that the Postfix process has the correct permissions to read the virtual mailbox map files. Incorrect permissions can sometimes cause Postfix to fail to read the configuration properly.

sudo chmod 644 /etc/postfix/vmailbox

7. Verify Virtual Domain Configuration

Make sure that the domain of the sender’s address is listed in the virtual_mailbox_domains parameter if it is a virtual domain.

By following these steps, you should be able to resolve the issue where Postfix rejects the sender address due to it being unknown in the virtual mailbox table. If the problem persists, you might want to consult Postfix documentation or seek additional support based on your specific setup.

Conclusion

The error message like Sender address rejected: User unknown in virtual mailbox table occurred from Postfix shows that Postfix error is continuously rejecting the same email again and again because it cannot discover the address of the sender in the virtual mailbox table. This problem usually occurs when the sender’s email address is not mentioned in the table that Postfix is currently using. For this, it is good to have managed ODOO server solutions.