No subscribed post or forum emails sending

Emails are not being sent when a new topic is made on a subscribed forum. No emails are being sent when someone responds to a a subscribed topic. Other emails such as tests in the admin and membership activation messages are sending as expected.

In this case I'm subscribed to a forum named "Getting Started". When a new post is made on that forum I never get a email.

In this case I'm not active in the forum when the post is created. I'm often inactive for long periods of time and I'm almost never logged in. I've tested by logging out and closing my browser then asking another user make a post to a forum I'm subscribed to. I get no email. When that user logs out and I log in and respond to that post, the user who made that post doesn't get an email.