Question : Exchange smtp gateway direct to internet

Hi experts,
I know its not best practice; but what are the "dangers" of using an exchange server as your incoming internet SMTP gateway in the following configuration?
Exchange server on NAT'd private subnet
Only protocol exposed are smtp and http
Only internal IP's can relay to gateway
Antispam - antivirus installed.

Answer : Exchange smtp gateway direct to internet

Here's the complete script:

                       
         
           
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             .left 
{ position :relative;
  
  
    background-image :url("images/leftIntro.png");
    background-repeat: no-repeat;
    height :380px;
    width:250px;
    float:left;
}

.left2 
{ position :relative;
  
  left:274px;
    background-image :url('images/leftIntro.png');
    background-repeat: no-repeat;
    height :380px;
    width:250px;
    top: -379px;
    float:left;
}		

</style>
</head>
<body>
    <form id="form1" runat="server">
    <div>
      <br />
        News
        <br />  <br />
        Select  a year level to find latest news
        <br />
        
        <div class="left">
        sasas
        </div>
        
         <div class="left2">
        sasas
        </div>
        <div style="clear:both;">&nbsp;</div>
           
         