shawfactor

mattsenate

This plugin is can be used for petitions, events, or any verified list and as far as I know is unique in WordPress.
Creating a petition/list/signup is as easy as adding a shortcode to a post or page (or CPT). From there additional editors are available to configure easch aspect of the sign up. Everything is completely self hosted and all list members become users of your site (not a third parties).
Available shortcodes:
[lh_signing_form] (enable signatories on any post, page, or custom post type)
Unconfirmed signatories: [lh_signing_unconfirmed_count]
Confirmed signatories: [lh_signing_confirmed_count]
Total signatories: [lh_signing_total_count]
[lh_signing_unconfirmed_list] (unformated list)
[lh_signing_confirmed_list] (unformated list)
You can customise the display of the signing form ([lh_signing_form]) via a number of shortcode arguments more information is available <a href="https://lhero.org/portfolio/lh-signing/" title="Additional Plugin documentation" rel="nofollow ugc">here</a>

LH Signing

LH Signing allows you to create configurable validated lists like petitions or event sign ups. It is the only self hosted solution in WP

emailable

Verify emails in real-time with Emailable.
Integrate with Emailable’s email verification API through this official plugin. Reduce spam and increase the quality of your signups by verifying emails directly from any form.
This is compatible with all major WordPress Forms and plugins that use the is_email function to validate email addresses. 
This includes, but is not limited to:
<ul>
<li>WordPress’s default registration and comment forms</li>
<li>WooCommerce’s registration and checkout form</li>
<li>Gravity Forms</li>
<li>Contact Form 7</li>
<li>Ninja Forms</li>
<li>Jetpack Forms</li>
</ul>
Emailable’s verification includes:
<ul>
<li>Disposable Email Detection</li>
<li>Accept-All Email Detection</li>
<li>MX Record Detection</li>
<li>SMTP Provider Details</li>
<li>Misspelled Domain Detection</li>
<li>Syntax Validation</li>
<li>Domain Validation</li>
<li>SMTP Verification</li>
<li>Email Deduplication</li>
<li>Role Email Detection</li>
<li>Free Email Detection</li>
<li>Email Quality Score</li>
<li>Anti-Greylisting Technology</li>
</ul>
To use this plugin, <a href="https://app.emailable.com/signup/" rel="nofollow ugc">sign up for a free Emailable account</a>, create an API key. All new signups will receive 250 free credits. 
What makes Emailable special?
<ul>
<li>Best in class performance: 30k emails verified per minute</li>
<li>Most Advanced Email Detection: Free, No Reply, Role, Accept-All, Disposable, and Mailbox Full</li>
<li><a href="https://emailable.com/guarantee/" rel="nofollow ugc">99%+ Deliverability Guarantee</a></li>
<li>99.99% Uptime</li>
<li>24/7 Support</li>
<li>SOC 2 Type II certified</li>
<li>GDPR, Privacy Shield, CCPA, and LGPD compliant</li>
</ul>
See more information about data privacy in the links below:
<ul>
<li><a href="https://emailable.com/terms-of-service/" rel="nofollow ugc">Emailable’s Terms of Service</a></li>
<li><a href="https://emailable.com/privacy-policy/" rel="nofollow ugc">Emailable’s Privacy Policy</a></li>
<li><a href="https://emailable.com/data-processing-agreement/" rel="nofollow ugc">Emailable’s Data Protection Agreement</a></li>
<li><a href="https://emailable.com/anti-spam-policy/" rel="nofollow ugc">Emailable’s Anti-Spam Policy</a></li>
</ul>

Emailable – Premium Email Verification & Validation

Verify emails in real-time with Emailable.

LH Signing vs Emailable – Premium Email Verification & Validation