UK Address Postcode Validation

This plugin will allow you to check your pages/posts HTML against the W3C Validator.

This plugin adds an awesome feature that provides instant feedback and guidance in each field, helps prevent errors.

Contact Form 7 Email Validation plugin adds an extended validation to verify domain in email address for email fields of Contact Form 7 plugin.

Added mail validation function to Contact Form 7. Protected by rejection filter, RFC filter, and DNS filter.

The Validated Field add-on for Advanced Custom Fields provides input masking and server-side validation of other field types.

With the Byteplant Phone Validator plugin you can easily verify if a phone number is really valid and callable (https://www.byteplant.