Neutrope Inc.

Neutrope Quiet Shield adds lightweight spam and unsolicited-sales filtering to 
Contact Form 7 submissions. The idea is simple: let spam and cold sales 
mail be received quietly without disturbing the people running the site.
Each submission is scored against a small set of checks you control:
<ul>
<li>Japanese character ratio: flag messages with too little Japanese text.</li>
<li>URL limit: flag messages that contain more links than you allow.</li>
<li>Submission speed: flag forms submitted suspiciously fast after they were 
shown. The timing value is signed so it cannot be tampered with.</li>
<li>Repeat submissions: flag three or more submissions from the same visitor 
within five minutes.</li>
<li>NG words: flag messages containing any keyword from your own list.</li>
</ul>
When a submission is flagged you choose what happens with Quiet Mode:
<ul>
<li>Quiet Mode on (default): the visitor sees the normal success message, but 
no mail is sent. The reason is written to the log.</li>
<li>Quiet Mode off: the submission is stopped with the standard Contact Form 
7 error message.</li>
</ul>
The plugin is deliberately small. It makes no external network requests, 
creates no database tables, and shows no ads or upsells. Configuration is 
stored in a single option, and the log keeps only decision metadata plus a 
short, salted IP hash. Message bodies, e-mail addresses and names are never 
stored.
If Contact Form 7 is not active, the plugin still activates safely and 
shows an admin notice instead of causing an error.
This plugin is an independent add-on and is not affiliated with or endorsed 
by the authors of Contact Form 7.
<h3>Features</h3>
<ul>
<li>Five independent checks, each configurable from one settings page.</li>
<li>Quiet Mode to silently drop flagged mail or stop it with an error.</li>
<li>Dashboard with today’s passed and blocked counts and a recent activity 
log.</li>
<li>Tamper-evident submission-speed measurement using a signed field.</li>
<li>IP addresses are hashed, never stored in raw form.</li>
<li>No external requests, no tracking, no database tables, no ads.</li>
<li>GPL-2.0-or-later. The full license text is bundled in the LICENSE file.</li>
</ul>
<h3>License</h3>
This plugin is licensed under the GPL-2.0-or-later. The full license text 
is included in the bundled LICENSE file. 
License URI: https://www.gnu.org/licenses/gpl-2.0.html

Neutrope Quiet Shield

Quietly deflect spam and unsolicited sales messages sent through Contact Form 7. Lightweight, no external calls, no stored personal data.

Yevhen Horbyshyn

This plugin adds a hidden “inverted” checkbox to your forms to prevent bots from submitting them.
<ul>
<li>Adds support for Contact Form 7 via shortcode <code>[ica_checkbox]</code></li>
<li>Adds JavaScript-based hidden checkbox to regular forms in the footer</li>
<li>Blocks form submission if the checkbox is unchecked or missing (typical behavior for bots)</li>
</ul>

Inverted Checkbox Antispam

Simple spam protection using an inverted checkbox. Compatible with Contact Form 7 and custom HTML forms.

Neutrope Quiet Shield vs Inverted Checkbox Antispam