A few possible improvements

When I wrote my first newsletter and pressed “test”, I first got a Wordfence warning and had to whitelist the request, then I got an error message that I had no test users defined, then my newsletter was lost and I had to re-type it!
* Please auto-save the newsletter as it is being written.
* Consider using the Gutenberg editor
* See if there is a way to auto-whitelist with Wordfence (probably the culprit for where the data was lost)
* Allow setting the test email addresses at the Newsletter UI, rather than the subscribers UI. I’ll want to test the newsletter with different email addresses each time, particularly mail-tester.com addresses

The settings are often unintuitive and could be helped with descriptions.
* Disable standard styles – I thought this would disable the dark-mode style of the UI… I’m not sure what it does
* What’s the difference between Log level: debug and Debug mode: yes
* Feed by mail
I’m not asking here what these do, e.g. there’s a documentation page for Feed by mail, but I suggest you add a quick explanation inline in the settings and link to the documentation.

The API TNP::unsubscribe() is good, but there’s no TNP::bounce().

I really don’t like the dark mode and would pay just to remove that!

When looking at https://www.thenewsletterplugin.com/premium I scroll down and try to click WooCommerce but it’s not a link. I have to use the menu to get to the WooCommerce detail page. There’s also a small spelling mistake on that page: “to comply with UE privacy laws” -> “EU”.

Thanks for a great plugin. I’m only getting familiar with it but it’s impressive so far.