WebInk Digital

This plugin is an add-on for the <a href="https://wordpress.org/plugins/booking/" rel="ugc">Booking Calendar</a> plugin and requires it to function (version 10.10.2 or newer).
It enhances booking security by introducing One-Time Password (OTP) verification via SMS or email. When a user attempts to confirm a booking, they are prompted to verify the action with an OTP, helping to ensure the authenticity of the request.
SMS verification is provided via the <a href="https://sms.to" rel="nofollow ugc">SMS.to</a> service. You must have an active SMS.to account and API key configured in the plugin settings to enable SMS delivery.
<h3>External Services</h3>
This plugin connects to an external service to send One-Time Passwords (OTP) via SMS as part of the booking verification process.
Service Used: <a href="https://sms.to" rel="nofollow ugc">SMS.to</a> 
What it’s used for: Sending OTPs (One-Time Passwords) via SMS during booking confirmations. 
What data is sent and when: 
– The recipient’s phone number 
– The OTP message content 
These are sent to the SMS.to API at the time a booking requires verification via SMS.
Terms of Service: https://sms.to/terms/ 
Privacy Policy: https://sms.to/privacy-policy/

OTP Add-on for Booking Calendar

Adds One-Time Password (OTP) verification via SMS or email to the Booking Calendar plugin for secure booking confirmations.

EverPress

Verifies your subscribers email addresses. Read more on the <a href="https://kb.mailster.co/reduce-false-signups-with-email-verification/?utm_campaign=wporg&utm_source=Email+Verify+for+Mailster&utm_medium=readme" rel="nofollow ugc">Mailster Knowledge base</a>
This plugin is no longer needed since Mailster 3.0!
<h3>Additional Info</h3>
<blockquote>
This Plugin requires <a href="https://mailster.co/?utm_campaign=wporg&utm_source=Email+Verify+for+Mailster&utm_medium=readme" rel="nofollow ugc">Mailster Newsletter Plugin for WordPress</a>
</blockquote>

Mailster Email Verify

The plugin will reject the email address if there is no such domain, but the SMTP ping to see whether the actual email address exists or not doesn't work.
Without this, it's not really useful.

MX checking works, SMTP doesn't

Verifies your subscribers email addresses. Read more on the Mailster Knowledge base

OTP Add-on for Booking Calendar vs Mailster Email Verify