Verify the milter configuration

Oct 13, 2025 by wbrum.org 0 views

Introduction

Postfix is a popular open-source mail transfer agent (MTA) that provides a robust and flexible email delivery system. One of the key features of Postfix is its support for mail filters, also known as milters. Milters are programs that can inspect and modify email messages as they pass through the Postfix mail server. However, when configuring milters, a common issue arises when using the per-milter action clause, which can cause Postfix's smtpd to fail. In this article, we will explore the per-milter action clause, its purpose, and how it can lead to smtpd failures.

Understanding Per-milter Action Clause

The per-milter action clause is a configuration option in Postfix that allows administrators to specify actions to be taken for specific milters. The clause is used in the smtpd_milters parameter, which specifies the milters that should be executed for incoming email messages. The per-milter action clause is typically used to specify the action to be taken when a milter returns a specific status code.

Per-milter Action Clause Syntax

The per-milter action clause syntax is as follows:

smtpd_milters = inet:localhost:8891,
    unix:/var/run/opendmarc/opendmarc.sock,
    unix:/var/run/openarc/openarc.sock,
    unix:/var/run/clamav-...,
    <milter_name> <action> <status_code>

In this syntax, <milter_name> is the name of the milter, <action> is the action to be taken, and <status_code> is the status code returned by the milter.

Common Issues with Per-milter Action Clause

When using the per-milter action clause, several issues can arise that can cause Postfix's smtpd to fail. Some of the common issues include:

Invalid milter name: If the milter name specified in the per-milter action clause is invalid, Postfix will fail to start.
Invalid action: If the action specified in the per-milter action clause is invalid, Postfix will fail to start.
Invalid status code: If the status code specified in the per-milter action clause is invalid, Postfix will fail to start.
Milter not found: If the milter specified in the per-milter action clause is not found, Postfix will fail to start.

Example of Per-milter Action Clause Configuration

Here is an example of a per-milter action clause configuration:

smtpd_milters = inet:localhost:8891,
    unix:/var/run/opendmarc/opendmarc.sock,
    unix:/var/run/openarc/openarc.sock,
    unix:/var/run/clamav-...,
    opendmarc accept 200

In this example, the per-milter action clause is used to specify that the opendmarc milter should be executed with the accept action and a status code of 200.

Troubleshooting Per-milter Action Clause Issues

If you encounter issues with the per-milter action clause, here are some troubleshooting steps you can take:

Check the Postfix logs: Check the Postfix logs for any error messages related to the per-milter action clause.
Verify the milter configuration: Verify that the milter configuration is correct and that the milter is running.
Check the milter status code: Check the status code returned by the milter to ensure it is valid.
Try removing the per-milter action clause: Try removing the per-milter action clause to see if the issue is resolved.

Conclusion

In conclusion, the per-milter action clause is a powerful configuration option in Postfix that allows administrators to specify actions to be taken for specific milters. However, when using the per-milter action clause, several issues can arise that can cause Postfix's smtpd to fail. By understanding the per-milter action clause syntax, common issues, and troubleshooting steps, administrators can ensure that their Postfix mail server is configured correctly and running smoothly.

Best Practices for Using Per-milter Action Clause

Here are some best practices for using the per-milter action clause:

Use valid milter names: Use valid milter names in the per-milter action clause.
Use valid actions: Use valid actions in the per-milter action clause.
Use valid status codes: Use valid status codes in the per-milter action clause.
Test the per-milter action clause: Test the per-milter action clause to ensure it is working correctly.
Monitor Postfix logs: Monitor Postfix logs for any error messages related to the per-milter action clause.

Common Milter Configuration Issues

Here are some common milter configuration issues that can cause Postfix's smtpd to fail:

Invalid milter configuration: An invalid milter configuration can cause Postfix's smtpd to fail.
Milter not found: If the milter specified in the milter configuration is not found, Postfix's smtpd will fail.
Milter not running: If the milter is not running, Postfix's smtpd will fail.
Milter configuration file not found: If the milter configuration file is not found, Postfix's smtpd will fail.

Troubleshooting Milter Configuration Issues

Here are some troubleshooting steps you can take to resolve milter configuration issues:

Check the Postfix logs: Check the Postfix logs for any error messages related to the milter configuration.
Verify the milter configuration: Verify that the milter configuration is correct and that the milter is running.
Check the milter status code: Check the status code returned by the milter to ensure it is valid.
Try removing the milter configuration: Try removing the milter configuration to see if the issue is resolved.

Conclusion

In conclusion, milter configuration issues can cause Postfix's smtpd to fail. By understanding common milter configuration issues and troubleshooting steps, administrators can ensure that their Postfix mail server is configured correctly and running smoothly.

Best Practices for Milter Configuration

Here are some best practices for milter configuration:

Use valid milter names: Use valid milter names in the milter configuration.
Use valid actions: Use valid actions in the milter configuration.
Use valid status codes: Use valid status codes in the milter configuration.
Test the milter configuration: Test the milter configuration to ensure it is working correctly.
Monitor Postfix logs: Monitor Postfix logs for any error messages related to the milter configuration.
Q&A: Using Per-milter Action Clause Causes Postfix's smtpd to Fail ====================================================================

Q: What is the per-milter action clause in Postfix?

A: The per-milter action clause is a configuration option in Postfix that allows administrators to specify actions to be taken for specific milters. It is used in the smtpd_milters parameter to specify the milters that should be executed for incoming email messages.

Q: What is the syntax for the per-milter action clause?

A: The syntax for the per-milter action clause is as follows:

smtpd_milters = inet:localhost:8891,
    unix:/var/run/opendmarc/opendmarc.sock,
    unix:/var/run/openarc/openarc.sock,
    unix:/var/run/clamav-...,
    <milter_name> <action> <status_code>

In this syntax, <milter_name> is the name of the milter, <action> is the action to be taken, and <status_code> is the status code returned by the milter.

Q: What are some common issues with the per-milter action clause?

A: Some common issues with the per-milter action clause include:

Invalid milter name: If the milter name specified in the per-milter action clause is invalid, Postfix will fail to start.
Invalid action: If the action specified in the per-milter action clause is invalid, Postfix will fail to start.
Invalid status code: If the status code specified in the per-milter action clause is invalid, Postfix will fail to start.
Milter not found: If the milter specified in the per-milter action clause is not found, Postfix will fail to start.

Q: How do I troubleshoot issues with the per-milter action clause?

A: To troubleshoot issues with the per-milter action clause, follow these steps:

Check the Postfix logs: Check the Postfix logs for any error messages related to the per-milter action clause.
Verify the milter configuration: Verify that the milter configuration is correct and that the milter is running.
Check the milter status code: Check the status code returned by the milter to ensure it is valid.
Try removing the per-milter action clause: Try removing the per-milter action clause to see if the issue is resolved.

Q: What are some best practices for using the per-milter action clause?

A: Some best practices for using the per-milter action clause include:

Use valid milter names: Use valid milter names in the per-milter action clause.
Use valid actions: Use valid actions in the per-milter action clause.
Use valid status codes: Use valid status codes in the per-milter action clause.
Test the per-milter action clause: Test the per-milter action clause to ensure it is working correctly.
Monitor Postfix logs: Monitor Postfix logs for any error messages related to the per-milter action clause.

Q: What are some common milter configuration issues that can cause Postfix's smtpd to fail?

A: Some common milter configuration issues that can cause Postfix's smtpd to fail include:

Invalid milter configuration: An invalid milter configuration can cause Postfix's smtpd to fail.
Milter not found: If the milter specified in the milter configuration is not found, Postfix's smtpd will fail.
Milter not running: If the milter is not running, Postfix's smtpd will fail.
Milter configuration file not found: If the milter configuration file is not found, Postfix's smtpd will fail.

Q: How do I troubleshoot milter configuration issues?

A: To troubleshoot milter configuration issues, follow these steps:

Check the Postfix logs: Check the Postfix logs for any error messages related to the milter configuration.
Verify the milter configuration: Verify that the milter configuration is correct and that the milter is running.
Check the milter status code: Check the status code returned by the milter to ensure it is valid.
Try removing the milter configuration: Try removing the milter configuration to see if the issue is resolved.

Q: What are some best practices for milter configuration?

A: Some best practices for milter configuration include:

Use valid milter names: Use valid milter names in the milter configuration.
Use valid actions: Use valid actions in the milter configuration.
Use valid status codes: Use valid status codes in the milter configuration.
Test the milter configuration: Test the milter configuration to ensure it is working correctly.
Monitor Postfix logs: Monitor Postfix logs for any error messages related to the milter configuration.