How to send notifications from the Plesk server when no mail components are installed?
In order to send notifications, Plesk uses the integration with mail components installed along with it.
When no mail components are available, Plesk is not able to communicate with the SMTP service and use it to send notifications or mail generated by user scripts.
In order to enable this functionality, it is required to perform the following:
Install MSMTP (Relay only) component via Tools & Settings > Updates.
Configure relaying mail server which will be used for sending notifications in Tools & Settings > External SMTP Server and make sure that Allow Plesk to send email notifications through this SMTP server is checked.