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How do I set directives for sending outgoing messages

on Plesk Postfix on Ubuntu 22.04?

To set custom directives for outgoing messages in Postfix on Plesk with Ubuntu 22.04, you can edit Postfix's configuration files to define how outgoing emails are handled. Here’s a step-by-step guide to help you apply these settings:

1. Access Postfix Configuration Files

In Plesk, Postfix configurations are generally managed in /etc/postfix/main.cf and /etc/postfix/master.cf. To modify these files:

    ```bash
    sudo nano /etc/postfix/main.cf
    ```

2. Set Outgoing Directives in main.cf

In the main.cf file, you can add or modify the following directives depending on your requirements for outgoing emails:

  • Set the myhostname:
    Ensure that your hostname is correctly set, as it will affect how emails are perceived by other servers (for example, to reduce spam rejection).

       ```bash
   myhostname = mail.yourdomain.com
   ```

  • Specify the relayhost (if relaying through another server):
    If you’re using an external relay for outgoing mail, specify it here.

       ```bash
   relayhost = [smtp.relayserver.com]:587
   ```

    Replace [smtp.relayserver.com]:587 with the relay server's address and port if needed.

  • Enable Authentication for Outgoing Mail (if using a relay):
    Set up SASL authentication if required for the relay server.

       ```bash
   smtp_sasl_auth_enable = yes
   smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
   smtp_sasl_security_options = noanonymous
   ```

    In /etc/postfix/sasl_passwd, you’ll add credentials like:

       ```plaintext
   [smtp.relayserver.com]:587    username:password
   ```

    Then, secure the file and update Postfix:

       ```bash
   sudo chmod 600 /etc/postfix/sasl_passwd
   sudo postmap /etc/postfix/sasl_passwd
   ```

  • Set Rate Limits for Outgoing Mail (Optional):
    You can limit the rate of outgoing emails to control spam and server load.

       ```bash
   default_destination_rate_delay = 5s
   default_destination_concurrency_limit = 2
   ```

3. Update master.cf for Outgoing Message Control

Edit /etc/postfix/master.cf to adjust the outgoing SMTP service, such as enabling submission on port 587:

    ```bash
    sudo nano /etc/postfix/master.cf
    ```

Uncomment or add the following block if needed:

    ```plaintext
    submission inet n       -       n       -       -       smtpd
       -o smtpd_sasl_auth_enable=yes
       -o smtpd_tls_security_level=encrypt
       -o smtpd_client_restrictions=permit_sasl_authenticated,reject
    ```

This setup enables the submission service on port 587 with TLS and SASL authentication.

4. Apply and Restart Postfix

After modifying main.cf and master.cf, restart Postfix to apply the changes:

    ```bash
    sudo systemctl restart postfix
    ```

5. Verify Configuration

Check the syntax of your configuration and any issues in the logs:

    ```bash
    sudo postfix check
    sudo tail -f /var/log/mail.log
    ```

This setup allows you to control outgoing mail settings, including specifying a relay host, applying rate limits, and enforcing authentication for outgoing emails.