Flector

The plugin sends you an email each time a comment goes to the spam folder. The plugin will come in handy in combination with anti-spam plugins like <a href="https://wordpress.org/plugins/antispam-bee/" rel="ugc">Antispam Bee</a>, <a href="https://wordpress.org/plugins/invisible-captcha/" rel="ugc">Invisible Captcha</a> and others that completely filter out comments from bots. It saves you the trouble of having to visit the “Spam” folder and manually check whether any real comments have been marked as spam by mistake.
We don’t recommend installing this plugin if you use <a href="https://wordpress.org/plugins/akismet/" rel="ugc">Akismet</a> only – you’ll be drowned in hundreds of emails every day.
If you liked my plugin, please rate it.

Spam Notifier

The plugin sends an email message when a comment goes to the spam folder.

OneOfOne

This plugin plugin blocks spam in comments automatically, without requiring any end-user input or any javascript.
<ul>
<li>As of version 0.7.7 there’s an option to add an extra javascript check, it’s off by default.</li>
</ul>
In a way it’s similar to webvitaly’s <a href="https://wordpress.org/plugins/anti-spam/" rel="ugc">Anti-Spam</a> however this doesn’t require the user to enter anything at all.
The comment gets marked as spam if any of the following rules are true :
<ul>
<li>If the comment is a trackback.</li>
<li>If the time between loading the page and commenting is less than 10 seconds.</li>
<li>If the Session variable specific to this form is not set.</li>
<li>If the hidden input field have a different value than “-“.</li>
<li>If the comment includes more than 3 urls.</li>
<li>If the referer isn’t set properly.</li>
</ul>
Once the comment gets flagged as spam, and if the auto delete option isn’t set, a json string will be appended to it to show why it was marked, for example :
<pre><code>{ "is-trackback": 0, "no-session-token": 0, "hidden-field": 1, "number-of-urls": 5, "referer": 0, "too-fast": 1.902538061142 } </code></pre>
Translates to :
<ol>
<li>They changed the hidden input field.</li>
<li>They Had 5 URLs in the comment.</li>
<li>It Took 1.9 seconds to submit the comment since the page was loaded.</li>
</ol>
Also note that the time calculations are per-form, so there are no false-positives if the user has multiple pages open on the site and commented on 2 of them in a short period of time.
Feel free to fork it and submit patches / fixes on <a href="https://github.com/OneOfOne/ooo-nospam" rel="nofollow ugc">github</a>

OneOfOne’s NoSpam

Extremely simple, 0 configuration and 0 user/admin-interaction anti-spam plugin.

Spam Notifier vs OneOfOne’s NoSpam