Unable to send email or connect to SMTP: connect #5 to subsystem private/rewrite: Connection refused

Symptoms

• Unable to send an email with the following error in /var/log/maillog file:

  postfix/qmgr[8738]: warning: connect #5 to subsystem private/rewrite: Connection refused
  postfix/pickup[8739]: warning: connect #5 to subsystem public/cleanup: Connection refused

Cause

Wrong configuration in the /etc/postfix/master.cf file

Resolution

1. Connect to the server via SSH

2. Create a backup for /etc/postfix/master.cf file:

   # cp -pr /etc/postfix/master.cf /etc/postfix/master.cf.$(date +'%Y-%m-%d_%T')

3. Copy /etc/postfix/master.cf file content from working instance of Plesk

4. Restart Postfix service:

   # systemctl restart postfix