Php script sending mail twice with different timestamp although called just once - php

Question

I've read many posts with a topic like my title express. But there's no help for me and I'm totally stuck. I'm using this chunk of code:
function acceptCallbackData() {
$body = "test";
$subject = "Message sent by php";
$to = "a-person#parascus.de";
$header = 'MIME-Version: 1.0' . "\r\n";
$header .= 'Content-type: text/html; charset=utf-8' . "\r\n";
$header .= 'From: another-person#parascus.de' . "\r\n";
$from = "another-person#parascus.de";
$host = "xxxx";
$username = "xxxx";
$password = "xxxx";
$headers = array ('From' => $from, 'Subject' => $subject, 'Content-type' => 'text/html; charset=utf-8');
require_once "Mail.php";
$smtp = Mail::factory('smtp', array ('host' => $host, 'auth' => true, 'username' => $username, 'password' => $password));
$mail = $smtp->send($to, $headers, $body);
$_SESSION["ERRORS"] = "";
exit();
}
I think the address of the "To" exists only once (not in the call and also the headers) and the exit() makes sure (and firebug tells me as well) that this script/function is executed only once.
But I still get the mail to times and there can be a different timestamp as well. Any suggestions how I can fix this problem?
Best regards
parascus

Answer 1

First thing when debugging PHP mail (when sending from a front-end javascript/jQuery/etc. client) is to remove the client from the equation.
Can you call the php function on its own and reproduce the duplicate mails? If not, then your problem lies with your front-end. If so, then you need to find where in your php code the function is being reproduced.
In this case, we determined that it was indeed client-side.