So ...

We are going to use a handy plugin called Thank Me Later.

Here it is:

https://wordpress.org/plugins/thank-me-later/

Note: you'll see the usual warning message saying that the plugin hasn’t been tested with the latest major releases of Wordpress ... Ignore it ... I've tested the plugin on Wordpress 5.1 and works fine.

As I said, the plugin sends Thank You emails to your blog commenters. Simply write a message saying thanks and it will be emailed after a time of your choice — five minutes, a day, a month, whenever! This way you can attract readers back to your blog and ask them to check for replies to their comments. Other uses of the plugin include links to your RSS feed, links to your Twitter or Facebook pages, discounted offers, etc.

Included features:

• HTML emails - write your email in text and it is changed into an HTML email with one click
• shortcodes - use shortcodes like [name] to make your emails more personal
• targeting - write emails for each category or post on your blog

It's a small plugin (204 KB), but let's see the usual speed tests ...

Here are my results before installing the plugin ...

... and the result after installing and activating the plugin:

No more comments needed ...

Now let's see how it works ...