Edit in JSFiddle

$('#submit').click(function() {  
 
    $(".error").hide();
    $("label").removeClass('red');

    var hasError = false;
    var emailReg = /^([\w-\.]+@([\w-]+\.)+[\w-]{2,4})?$/;
    var name = $('#name').val();
    var message = $('#message').val();
    var emailaddressVal = $("#email").val();
    if(emailaddressVal == '') {
      $("#email").after('<small class="error small">Please enter your email address</small>');
      $("label[for=email]").addClass('red');
      hasError = true;
    }

     if(!emailReg.test(emailaddressVal)) {
      $("#email").after('<small class="error">Enter a valid email address</small>');
      $("label[for=email]").addClass('red');
      hasError = true;
    }
 
 
    if(hasError == true) { return false; }
 
    });

<form >
<label for="email">Email:</label>
<input type="text" name="email" id="email">
<input type="submit" id="submit"/>
</form>

body {font-family: sans-serif;}
.red { color:red }
.error { color: red; display:block;}
input {display:block; margin: 5px 0}