I am new to developing sites, I have created a form with a persons contact details. 

In the email text field I would like to only allow email addresses with the character @, if the '@' character is not present, then an error message will be displayed. 

Html code for email entry is:

```
<td class="content"><input name="txtEmail" type="text" class="box" id="txtEmail" size="60" maxlength="100" /></td>

```

Javascript to ensure that the field is entered is:

```
function checkShippingAndPaymentInfo()
{
    with (window.document.frmCheckout) {
        if (isEmpty(txtEmail, 'Please enter your email address')) {
            return false;
        } else {
            return true;
        }
    }
}

```

The code above works but does not have the restriction I require. All I need is validation for the '@' character to be set in the text entry field. Please can someone help me with this. 

Thank you in advance.