PHP mail() cannot send mail on Plesk server: The user user is not allowed to send email

kb: bug Plesk for Linux

Applicable to:

The server is set to Allow users and scripts to use Sendmail at Tools&Settings > Mail Server Settings
The subscription created is based on a Service Plan with Mail service disabled
Emails sent using the PHP mail() function are not delivered.

Plesk bug PPPM-12408. In the /var/log/maillogthe following error can be found:

CONFIG_TEXT: Rejecting message: system user is not allowed to send mail

As a workaround:

Click on a section to expand

Via GUI:

Via CLI:

Connect to the server via SSH
Execute the following command to enable and disable mail service for domain:

# plesk bin mail --create-service example.com && plesk bin mail --off example.com

For all domains:

Connect to the server via SSH
Create script phpmail.sh and start editing it:

# vi /root/phpmail.sh
Add the following content to it and save changes:

CONFIG_TEXT: #!/bin/bash
echo "--------------" >> /tmp/event_handler.log
/bin/date >> /tmp/event_handler.log
/usr/bin/id >> /tmp/event_handler.log
PLAN_NAME=$(plesk bin site --info ${NEW_DOMAIN_NAME} | egrep Subscription\ Information -A5 | egrep service\ plan | cut -d'"' -f2)
MAIL_ACTIVE=$(plesk bin service_plan --info "$PLAN_NAME" | egrep Settings -A5 | egrep Mail\ | awk '{print $2}')
echo "${NEW_DOMAIN_NAME} -> $PLAN_NAME / Mail Service = $MAIL_ACTIVE" >> /tmp/event_handler.log
if [ "$MAIL_ACTIVE" == "false" ]; then
echo "ACTION => Create service + switch off" >> /tmp/event_handler.log
plesk bin mail --create-service ${NEW_DOMAIN_NAME}
plesk bin mail --off ${NEW_DOMAIN_NAME}
fi
echo "--------------" >> /tmp/event_handler.log
Make the script executable:

# chmod +x /root/phpmail.sh
Log in to Plesk
Go to Tools&Settings > Event Manager > Add event handler and add the event as follows:
Click OK to save changes.