The email-ext plugin allows users configuring jobs on a controller to modify the 'from' attribute at a job level (using Pipeline `from:` , or freestyle `Project From`).

Some companies have internal policies which do not allow this.

Definition of done:

The 'from' field of emails sent by the email-ext plugin should always use the `from` address defined at `Manage Jenkins` -> `System` -> `System Admin e-mail address`, and not be configurable at a job-level.

Not all users will want to enable this restriction, so an optional system property to enable this feature should be added.

Emitting an informational message to the controller logs when the 'from' field is used by a job would also be helpful to see when the feature is active.