Plesk notifications are not sent: Postfix is running with backwards-compatible default settings

Symptoms

• Notifications which are set up in Plesk in Tools & Settings > Notifications are not sent.

• In Tools & Settings > Mail Server Settings, Postfix is set up as SMTP server:
  

• The following records can be found in the file /var/log/maillog:

  postfix[54992]: Postfix is running with backward-compatible default settings
  plesk postfix/master[32815]: terminating on signal 15 
  plesk postfix[55085]: Postfix is running with backwards-compatible default settings 
  plesk postfix[55085]: See http://www.postfix.org/COMPATIBILITY_README.html for details 
  plesk postfix[55085]: To disable backwards compatibility use "postconf compatibility_level=2" and "postfix reload"

• Postfix was installed on server before Plesk installation;

• When connected to server via SSH, the configuration file like /etc/postfix/main.cf.rpmnew can be found. This file indicates that configuration files were modified before Plesk installation.

Cause

Postfix is running in the backward-compatible mode: on.
Upgrade done by the package manager backed up modified configuration files where backward-compatible mode was disabled and created new clean one.

Resolution

Note: This article is intended for use by server administrators. In case there is no administrative SSH access to the server, contact the server administrator or server provider.

1. Connect to the server using SSH.

2. Add the following line to the file /etc/postfix/main.cf:

   compatibility_level=2

3. Reload Postfix configuration:

   # service postfix reload