1. <form action="./includes/contact/contact-process.php" method="post" class="contact-form wpcf7-form">

$error = false;
$fields = array( 'name', 'email', 'subject',  'phone', 'message' );

foreach ( $fields as $field ) {
    if ( empty( $_POST[$field] ) || trim( $_POST[$field] ) == '' )
        $error = true;
}

if ( ! $error ) {
    $name = stripslashes( $_POST['name'] );
    $email = trim( $_POST['email'] );
    $subject = stripslashes( $_POST['subject'] );
$message = stripslashes( $_POST['message'] );
$phone =$_POST['phone'];

$msge .= "Nombre del remitente:".$name."rn";
$msge .= "Correo:".$email."rn";
$msge .= "Teléfono:".$phone."rn";
$msge .= "Mensaje:".$message."rn";

    $mail = mail( WEBMASTER_EMAIL, $subject, $msge,
         "From: " . $name . " <" . $email . ">rn"
        ."Reply-To: " . $email . "rn"
        ."X-Mailer: PHP/" . phpversion()
        );

    if ( $mail ) {
        echo "Success";
    } else {
        echo "Error";
    }
}
?>

и еще есть вот такая функция
  ajaxContactForm: function() {
            if ( $().validate ) {
                $('.contact-form').each(function() {
                    $(this).validate({
                        submitHandler: function( form ) {
                            var
                            $form = $(form),
                            str = $form.serialize();

                            $.ajax({
                                type: "POST",
                                url:  $form.attr('action'),
                                data: str,
                                beforeSend: function () {
                                    $form.find('.bwp-alert').remove();
                                },
                                success: function( msg ) {
                                    var result, cls;

                                    if ( msg == 'Success' ) {
                                        result = 'Su mensaje ha sido enviado';
                                        cls = 'success';
                                    } else {
                                        result = 'Su mensaje NO ha sido enviado';
                                        cls = 'error';
                                    }

                                    $form.prepend(
                                        $('<div />', {
                                            'class': 'bwp-alert ' + cls,
                                            'text' : result
                                        }).append(
                                            $('<a class="remove" href="#"><i class="fa fa-close"></i></a>')
                                        )
                                    );

                                    $form.find(':input').not('.submit').val('');
                                }
                            });
                        }
                    });
                });
            }
            $(document).on('click', '.bwp-alert .remove', function(e) {
                $(this).parent().slideUp();

                e.preventDefault();
            })
        },
плюс валидация в отдельном документе:

/*! jQuery Validation Plugin - v1.11.1 - 3/22/2013n* https://github.com/jzaefferer/jquery-validation
* Copyright (c) 2013 Jörn Zaefferer; Licensed MIT */(function(t){t.extend(t.fn,{validate:function(e){if(!this.length)return e&&e.debug&&window.console&&console.warn("Nothing selected, can't validate, returning nothing."),void 0;var i=t.data(this[0],"validator");return i?i:(this.attr("novalidate","novalidate"),i=new t.validator(e,this[0]),t.data(this[0],"validator",i),i.settings.onsubmit&&(this.validateDelegate(":submit","click",function(e){i.settings.submitHandler&&(i.submitButton=e.target),t(e.target).hasClass("cancel")&&(i.cancelSubmit=!0),void 0!==t(e.target).attr("formnovalidate")&&(i.cancelSubmit=!0)}),this.submit(function(e){function s(){var s;return i.settings.submitHandler?(i.submitButton&&(s=t("<input type='hidden'/>").attr("name",i.submitButton.name).val(t(i.submitButton).val()).appendTo(i.currentForm)),i.settings.submitHandler.call(i,i.currentForm,e),i.subm.....

<?php
define( "WEBMASTER_EMAIL", 'info@.com' );

$error = false;
$fields = array( 'name', 'email', 'subject',  'phone', 'message' );

foreach ( $fields as $field ) {
    if ( empty( $_POST[$field] ) || trim( $_POST[$field] ) == '' )
        $error = true;
}

if ( ! $error )
{
    $name = stripslashes( $_POST['name'] );
    $email = trim( $_POST['email'] );
    $subject = stripslashes( $_POST['subject'] );
    $message = stripslashes( $_POST['message'] );
    $phone =$_POST['phone'];

$msge .= "Nombre del remitente:".$name."rn";
$msge .= "Correo:".$email."rn";
$msge .= "Teléfono:".$phone."rn";
$msge .= "Mensaje:".$message."rn";

    $mail = mail( WEBMASTER_EMAIL, $subject, $msge,
         "From: " . $name . " <" . $email . ">rn"
        ."Reply-To: " . $email . "rn"

        ."X-Mailer: PHP/" . phpversion()

        );

    if ( $mail )
{
        echo "Success";


    $host='localhost';
    $db='';
    $user='';
    $pass='';
    $charset='utf8';


   // Create connection
$conn = new mysqli($host, $user, $pass, $db);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

   $sql="insert into bd_clientes( name, email, phone, subject, message) values ('$name', '$email','$phone','$subject', '$message')";

if ($conn->query($sql) === TRUE) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

$conn->close();



    }

    else {
        echo "Error";
    }
}


?>