I no longer get email notifications when a reply is posted to my threads

I used to be notified via email when someone posted a reply to my threads. For quite some time I have not received any such notifications. They are not going to my spam folder.

It would certainly make it easier to make timely responses if I were to get an email notice of a reply. Otherwise, I have to remember to check the thread periodically to see if there are any new responses.

Is there some reason I no longer get email notifications?