email - php mail() two copies sent

Question

I have a simple message that I send using php mail(). The code used:

//recipient info
$to = "$bookernavn <$mail>";
$from = "Visens Venner Hiller?d <booking@eksample.dk>";
$subject = "Kvittering - $a_titel - ". date("j/n - Y",$a_dato);

$headers  = "MIME-Version: 1.0" . "
";
$headers .= "Content-type: text/html; charset=utf-8" . "
";
$headers .= "From: $from" . "
";
$headers .= "Reply-To: $from" . "
";
$headers .= "Return-Path: $from" . "
";
$headers .= "Bcc: $from" . "
";

// now lets send the email. 
mail($to, $subject, $mailmsg, $headers); }

For some strange reason two mails are sent each time...
Sometimes with several minutes in between...
Any ideas?

Answer 1

You don't check to see if the form has been submitted so a browser refresh will send the form data again and cause the mail to be sent again. This also happens when a user presses the back button.

After the email is sent you need to do a 303 redirect to prevent the re-submission. You can redirect to the same page if you'd like.

This is called the Post/Redirect/Get pattern.

mail(...);
header('Location: /some-page-php', true, 303);
exit;