Emails are being sent by moodle with the noreply emailaddress instead of the user emailaddress.
The cause is that the users are not enroled with the same enrolment method.

Prereqs:
The teacher have got an emailadress with an allowed domain to send emails from.
The teacher and the student are not together in a course.
The student set up the notification preferences to get subscribed forum posts via email on- and offline.

Test steps:
1. Enrol a teacher in a course with manual enrolment
2. Enrol a student in a course with another enrolemnt mehtod may be with global groups
3. In the course, the teacher set up a forum with auto subscription
4. The teacher is posting a message in the forum.
5. The student will get the forum post via email and recognize that the post was sent via noreply address instead of the emailaddress of the teacher.

Cause:
The function call of enrol_get_shared_courses in the function can_send_from_real_email_address returns only "true" if the users are enrolled by the same enrolment method.