Post notification emails stuck in queue

You might want to check under Options / Cron Details to see if the tasks are actually being triggered. Note the times there are in GMT and not local time. There are, as I recall, 2 methods of possible correction:

1. Deactivate the plugin and activate it again to re-create the cron tasks.
2. Don’t use WP-CRON, but create a separate cron task to fetch the URL listed on that page.

I use the second option because it’s simply more reliable.

Thank you, we will try option 2!

This has happened to me a few times. Can you explain more about an alternative CRON task?

Sure. We run our own server, so I use native cron to do this. Assuming you are hosted somewhere, your webhost may or may not allow you to schedule cron jobs. Of course, it doesn’t need to happen on the same machine as the server–just somewhere that will be able to repeatedly fetch a web page.

Since I use cron, I created a bash script that runs something like this:
curl -H 'Cache-Control: no-cache, no-store' -H 'User-Agent: cron-email-posts-script-1.0' https://site-url/?elp=cron&guid=xxxxxxxxxxxxxx

You can find the URL part on the end in your WordPress control panel under Email Posts / Options on the Cron Details tab. I tell it not to cache so I’m sure it will look at the server every time, and use a custom user agent so I can see it in the access log. You can, of course, do less and just use curl followed by the URL. There is no output, so no reason to save it anywhere.

I run mine every 15 minutes so there isn’t a long delay between when a post gets published and when the emails start to go out.

Also, on that Cron Details tab, is a link or more information on how to set it up in common control panels and if you need to install something to schedule jobs yourself. I am personally fluent enough in Linux systems not to need the instructions, but if you’re not, you might find them helpful.