PHP- Send Mail after some Validation - php

Question

I am new to PHP not an expert by any means. Anyhow, I am building a PHP and HTML contact form and I am getting mixed up on the way to validate field input (trim, strip, htmlspecchars..). Anyways, here is my code, please go easy on me, I am a noob at this.
<?php
// define variables and set to empty values
$name = $email = $web = $telephone = $pages = $completion_date = $update_option = $hosting_option = $domain_option = $text = "";
if ($_SERVER["REQUEST_METHOD"] == "POST") {
$name = test_input($_POST["name"]);
$email = test_input($_POST["email"]);
$web = test_input($_POST["web"]);
$telephone = test_input($_POST["telephone"]);
$pages = test_input($_POST["pages"]);
$completion_date = test_input($_POST["completion_date"]);
$update_option = test_input($_POST["update_option"]);
$hosting_option = test_input($_POST["hosting_option"]);
$domain_option = test_input($_POST["domain_option"]);
$text = test_input($_POST["text"]);
}
function test_input($data) {
$data = trim($data);
$data = stripslashes($data);
$data = htmlspecialchars($data);
return $data;
}
$msg = $name . "\n";
$msg = $email . "\n";
$msg = $web . "\n";
$msg = $telephone . "\n";
$msg = $pages . "\n";
$msg = $completion_date . "\n";
$msg = $update_option . "\n";
$msg = $hosting_option . "\n";
$msg = $domain_option . "\n";
$msg = $text . "\n";
$recipient = "myemail#mydomain.com";
$subject = "Contact Has Been Made..";
$mailheaders = "MIME-Version: 1.0" . "\r\n";
$mailheaders = "Content-type:text/html;charset=iso-8859-1" . "\r\n";
$mailheaders = "From: <myemail#mydomain.com>, Reply-To: <myemail#mydomain.com>" . "\r\n";
$mailheaders = "Cc: <$email>" . "\r\n";
mail($recipient, $subject, $msg, $mailheaders);
?>

Answer 1

It looks okay until the definition of $msg, you keep overwriting it.
Prepend the equals (=) signs after the first with a dot (.)
$msg = $name . "\n";
$msg .= $email . "\n";
$msg .= $web . "\n";
... etc

Answer 2

stripslashes and htmlspecialchars are unnecessary in this context. After all, you are not outputting any HTML that contain the POSTed values.
The problem with your form validation is that I could write anything in the email field, for example, and it would still validate. You should make a case-by-case validation for all the fields so, for example with the email field
if (filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) {
// The email is valid
$email = $_POST['email'];
}
And so on. If you don't need them to be what they say the are, you can omit this. Other than that it looks okay.