Add a double email check field to Contact Form 7.
Kick spam with a highly advanced email validation in comment forms, user registration and contact forms using Mailgun's Email validation service.
LH Signing allows you to create configurable validated lists like petitions or event sign ups. It is the only self hosted solution in WP
With the Byteplant Email Validator plugin you can easily verify if an email address really exists and is valid (http://www.email-validator.net).
WP Valid Email is a WordPress plugin which offers suggestions to users who mis-type their email address when entering it on your website.
Provides better email validations to protect your blog from spam comments and bots creating accounts.
This plugin validates the existence of the domain name that is entered in the email address while checkout for WP e-Commerce store owners.
LH Teams creates a cpt called a team, this is effectively a configurable validated list of users, which can be managed by the author