/etc/postfix/

The /etc/postfix/ directory is the primary configuration directory for Postfix, a popular open-source mail transfer agent (MTA) used for routing and delivering email. Below is an overview of the key configuration files commonly found in this directory, including their purposes and basic usage.

Key Configuration Files in /etc/postfix/

1. main.cf

   • Purpose: This is the primary configuration file for Postfix. It defines the main settings and parameters for the Postfix mail server.

   • Common Parameters:

     • myhostname: The hostname of the mail server.

     • myorigin: The domain name that Postfix will append to mail addresses.

     • inet_interfaces: The network interfaces on which Postfix will listen for incoming mail.

     • mydestination: The domains that Postfix will deliver mail for.

   • Example Entry:

     myhostname = mail.example.com
     myorigin = example.com
     inet_interfaces = all
     mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain

2. master.cf

   • Purpose: This file configures the Postfix daemon processes and their options. It defines how Postfix handles incoming and outgoing mail through different services.

   • Common Services:

     • smtp: The service for handling outgoing mail.

     • submission: The service for handling mail submissions from clients.

     • smtpd: The service for handling incoming mail.

   • Example Entry:

     smtp      inet  n       -       n       -       -       smtpd
     submission inet n       -       n       -       -       smtpd

3. aliases

   • Purpose: This file defines email address aliases. It maps email addresses to local user accounts or other email addresses.

   • Common Use:

     • Redirecting mail for a specific address to another address or user.

   • Example Entry:

     postmaster: root
     abuse: root

4. canonical

   • Purpose: This file is used to define canonical (standardized) forms of email addresses. It maps addresses from their original form to a canonical form.

   • Example Entry:

     [e-mail]    [e-mail]

5. virtual

   • Purpose: This file is used for virtual domain handling. It maps virtual email addresses to local user accounts or other email addresses.

   • Example Entry:

     [e-mail]   user1
     [e-mail]   user2

6. main.cf.sample

   • Purpose: This is a sample configuration file provided by Postfix, used as a reference for setting up the main.cf file. It contains default settings and example configurations.

   • Usage: It can be copied to main.cf and modified as needed.

7. master.cf.sample

   • Purpose: This is a sample configuration file for the master.cf file. It provides example configurations for Postfix services.

   • Usage: It can be copied to master.cf and customized.

8. smtp_header_checks

   • Purpose: This file is used to define header checks for outgoing mail. It allows modification or filtering of email headers.

   • Example Entry:

     /^Subject:.*Spam/ DISCARD

9. smtpd_sender_restrictions

   • Purpose: This file contains restrictions on the sender of incoming mail. It is used to implement policies such as blocking or allowing specific senders.

   • Example Entry:

     permit_mynetworks
     reject_unauthenticated_sender

10. smtpd_recipient_restrictions

    • Purpose: This file defines restrictions on the recipients of incoming mail. It is used to enforce policies on email delivery.

    • Example Entry:

      permit_mynetworks
      reject_unauth_destination

11. postfix-main.cf

    • Purpose: This file is an alternate name sometimes used for main.cf and contains main configuration parameters for Postfix.

12. postfix-master.cf

    • Purpose: This file is an alternate name sometimes used for master.cf and defines the Postfix daemon processes.

Example Workflow

1. Edit Configuration Files:

   • Modify /etc/postfix/main.cf and /etc/postfix/master.cf to configure Postfix according to your needs.

2. Reload Configuration:

   • After making changes to the configuration files, reload Postfix to apply the new settings:

     systemctl reload postfix

3. Verify Configuration:

   • Check the status of Postfix to ensure it is running correctly:

     systemctl status postfix

4. Test Mail Flow:

   • Send a test email to verify that the mail server is functioning as expected.

Conclusion

The /etc/postfix/ directory contains essential configuration files for the Postfix mail server. Understanding and configuring these files properly ensures that Postfix can effectively handle mail delivery and routing for your system. Regularly reviewing and updating these configurations, along with monitoring mail server performance, is key to maintaining a robust and secure mail system.