Sending e-mail

If the problem is with getting the check box values;

here is the solution
[html]

<form id="form1" name="form1" method="post" action="mail_script.php">
<input type="checkbox" name="email[]" value="email1@domain.com"/>
<input type="checkbox" name="email[]" value="email2@domain.com"/>
<input type="checkbox" name="email[]" value="email3@domain.com"/>

<input type="submit" name="button" id="button" value="Submit" />

</form>
[/html]

[PHP]
<?php
$mail = $_POST['email'];
var_dump($mail);
?>
[/PHP]

on selecting 1st and 3rd checkboxes, output will be
If the problem is with mail function;
You can pass multiple email addresses to php's mail function. read the manual here
http://www.php.net/function.mail

And finally, I highly recommend you to use phpmailer for better performance.