Jordi Cabot

In the Settings->Discussion page, authors of a post can use the checkbox Email me whenever – Anyone posts a comment.
But this does not send an email as well to the site admins. In blogs where you have a number of guest authors, you may want to be informed about all the new comments so you can respond (if the author is missing) or just participate in the discussion.
As a site admin myself, I was missing many comments. This means plenty of missing opportunities to engage with your audience.
To solve this situation, the plugin adds a new checkbox in the Discussion page. If checked, admins will get an alert email for new comments.

Comment Admin Notifier

Very simple plugin that doesn't try to do many things. But the one it does is very useful: as a website owner you want to make sure you're on top of all the comments in the site even comments to posts you didn't write. 

It does one thing and it does it right

With this plugin, admin users get an email alert every time a new comment is posted on ANY post in the site.

Abu Hayat

bPlugins

Charles Cormier

Md. Merajul Islam Sojib

Create and display notices/alerts on the page using the Gutenberg block. it comes up with a few customizable options to design the alert box as you want. Improve the user experience of your website using this block plugin.
<a href="https://bblockswp.com/demo/alert" rel="nofollow ugc">Demos</a>
<h4>Features</h4>
<ul>
<li>Fully Customizable: Lots of options available to make the alert box as you want!</li>
<li>Different Types: Alert box block comes with different types, you can easily switch the type of alert box.</li>
<li>Standard Preset: Some preset alerts/notices are ready to use without any modification. </li>
</ul>
<h4>How to use</h4>
<ul>
<li>First, install the Alert Box Block plugin</li>
<li>Add the Alert Box Block from the block category called “Widgets” in the Gutenberg editor.</li>
<li>You can change block settings from the right-side settings sidebar.</li>
<li>
Enjoy!
</li>
<li>
For installation help click on Installation Tab
</li>
</ul>
<h4>Feedback</h4>
<ul>
<li>Did you like this plugin? Dislike it? Do you have a feature request? <a href="mailto:support@bplugins.com" title="Send feedback" rel="nofollow ugc">Please share your feedback with us</a></li>
</ul>
<h3>Check out the Parent Plugin of this plugin-</h3>
<a href="https://bblockswp.com" rel="nofollow ugc">B Blocks</a> – A blocks collection and page building tool for Gutenberg.
<h3>Check out our other WordPress Plugins-</h3>
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<a href="https://bplugins.com/products/pdf-poster/" rel="nofollow ugc">PDF Poster</a> – Display/Embed PDF files with different styles.
<a href="https://bplugins.com/products/html5-audio-player/" rel="nofollow ugc">Html5 Audio Player</a> – Listen audios with awesome visuals.
<a href="https://bplugins.com/products/streamcast-radio-player/" rel="nofollow ugc">StreamCast</a> – Customizable radio player with different skins.
<a href="https://bplugins.com/products/3d-viewer/" rel="nofollow ugc">3D Viewer</a> – Embed 3D models and 3D products with interaction.
<a href="https://bplugins.com/products/advanced-post-block/" rel="nofollow ugc">Advanced Post Block</a> – Show posts and custom posts in different layouts.

Alert Box Block – Display Custom Alerts and Messages

It's Very useful and handy for Gutenberg lover.

Comment Admin Notifier vs Alert Box Block – Display Custom Alerts and Messages