There are 2 ways to activate php mail on our Plesk server:

- At the server level: This is done from Tools and Settings > Mail Server Settings > Enable the option "Allow users and scripts to use Sendmail" > Accept. This will activate it for all domains on the server:

- At the subscription level: We go to Tools and Settings > Outgoing Mail Control > Click on Subscriptions > Then click on the domain where we want to activate it > Click on Change Limit > In the "Sendmail usage policy" option > Custom settings for the subscription > Allow the use of Sendmail for scripts and users in this subscription. We explain it with an image:

We can also do the same to deactivate it, by unchecking the allow options.