This could be for a number of reasons.
For customers and business admins, please first check that you have enabled / haven't disabled notifications. You can do this from your Profile>Notifications page.
Please check that your correspondence email is correct. You can check this under Profile>Edit Profile
Please check that the emails have not gone to your Junk folder
For business admins, please note that it is the set host instructor of a session who receives booking and cancellation emails, so please check you have set that field in the session set-up fields. If you are not the host instructor but still want to receive the emails you can ask the host to amend their correspondence email address.
If you do not think the above explain the issue please contact us at firstname.lastname@example.org noting your configured email address and we'll look into whether there was a delivery issue to your email provider.