Ok, so first the XHTML code is missing the <form> label, here's the code
<form action="mail.php" method="post">
<select name="cboMails">
<option value="mail1@test.com">mail1@test.com</option>
<option value="mail2@test.com">mail2@test.com</option>
<option value="mail3@test.com">mail3@test.com</option>
<option value="mailN@test.com">mailN@test.com</option>
</select>
<input type="submit" value="Submit" />
</form>
Quoting
W3Schools: "The most important thing to notice when dealing with HTML forms and PHP is that any form element in an HTML page will automatically be available to your PHP scripts."
This means that we will be able to access the data from any script using the $_POST['cboMails'] global variable, in our script we can retrieve the selected mail and send the info to it.
Here is the mail.php file:
<?php
$to = $_POST['cboMails'];
$subject = "Test mail";
$message = "Information to be mailed";
$from = "mywebsite@mymail.com";
$headers = "From: $from";
mail($to,$subject,$message,$headers);
echo "Mail Sent.";
?>
Notice how we've accessed the selected mail in the global $_POST[] variable (line 2 of the PHP code)
This is basically how to do it, this, however is insecure, since we don't validate any data and malicious users can inject the Cc, Bcc headers to send the information to other mail recipients check this link for
secure email 
Unsolved 
