by Lynn Hadfield.
Has the teacher tried a different email address (just in case that one is blocking the messages) perhaps outside the institution's email system (e.g. a gmail address)?
Does the teacher get notifications when quizzes are submitted or posts are made to forums?
Is it a custom role or the default 'teacher' role?
Does the teacher have more than one role in the course?
Just some things to help narrow down the issue.