Contact Form 7 - Make sure the emails in 2 different fields don't match.

functions.php

add_filter( 'wpcf7_validate_email*', 'custom_email_confirmation_validation_filter', 20, 2 );
function custom_email_confirmation_validation_filter( $result, $tag ) {
    $tag = new WPCF7_FormTag( $tag );
 
    if ( 'your-email' == $tag->name ) {
        $your_email = isset( $_POST['your-email'] ) ? trim( $_POST['your-email'] ) : '';
        $manager_email = isset( $_POST['manager-email'] ) ? trim( $_POST['manager-email'] ) : '';
 
        if ( $your_email == $manager_email ) {
            $result->invalidate( $tag, "Your email can NOT match your manager's email." );
        }
    }
 
    return $result;
}