If you want to check if it is empty, Here is a suggestion.
Please note: Once the text is outputted that the email address is empty, it will "Kill" the code from so on. So please note that if you want to do more "Checks" and do not want to kill it yet, do something else.
// Put the Form Code Here - Have the form's "Action" direct to something like form.php?act=check
$name = $_POST["name"];
$address = $_POST["address"];
$city = $_POST["city"];
$state = $_POST["state"];
$zip = $_POST["zip"];
$phone = $_POST["phone"];
$email = $_POST["email"];
$comments = $_POST["comments"];
// Empty Feilds
Echo"Your email address is required. Click <a href=''>here</a> to go back.";
$today = date("M d, Y");
$recipient = "email@example.com";
$subject = "Free Buyers Report Request";
Form Submitted: $today\n\n";
$formsend = mail("$recipient", "$subject", "$forminfo", "From: $email\r\nReply-to:$email");
<!-- The rest of the site-->
But, using the case's and switches allow you to break away without exiting etc.
Also - Remember, the form actions "?act=" has to be the case as the case"": or it will not work. Some smarter person will probably come in here and say i'm wrong, but thats okay lol