Unable to send emails with PHP scripts or Plesk notifications: /usr/sbin/sendmail No such file or directory

Symptoms

• Unable to send emails with PHP scripts in Plesk with the following error in the log file /var/log/plesk-php*-fpm/error.log:

  # egrep -Ri sendmail /var/log/plesk-php*-fpm/error.log
  WARNING: [pool example.com] child 29450 said into stderr: "sh: /usr/sbin/sendmail: No such file or directory"

• Plesk notifications, like an activation email, are not sent and the following error is shown in the log file/var/log/plesk/panel.log file:

  ERR [panel] Unable to send mail: Unknown error
  ERR [panel] Failed to send activation link due to: Unable to send mail: Unknown error

• Tools and Settings > Mail Server Settings shows that the installed mail server is Qmail

Cause

Sendmail symlinks to the Plesk Qmail wrapper are missing or invalid

Resolution