Lead Follow-up doesn't send email

Hello.

I’m not sure whether this is as-designed, or that something is wrong in my setup, but my understanding is Lead follow-up details should send an email notification at the specified date and time. If that is correct, what would be the reason I’m not getting a notification on this, when all other notifications are received.

Please enter next follow up date then you will receive an email before one night of the next follow up date