Hello Tony,
Thanks for writing in today with your question. Sorry to hear those emails aren’t getting through.
Email issues are generally outside the scope of the GD plugin, as this is usually an issue situated between your host and your email sending agent, if you have one.
To get you started on a diagnosis, first off it’s great you have already verified that the notifications are being created with the mail-log plugin. That’s definitely the first step.
The next step is to find out if your site is sending any email that is being received at all. Is this issue also stopping new registration emails, too, then? And password reset emails? If so, then this is definitely an issue to take up with your host. Please make a ticket with your host and let us know the result of that.
You can make a private reply here to share your site URL so we can take a look, but without meaning to sound negative, we will likely only be able to verify what you have found so far.