PHP mail function - Hide email id's


I am trying to use the php send mail function and have the following question.
I am sending mail to multiple recpients(3-5). I do not want any of the user to see all the other email addressess and so I added the BCC option. I added the "senders" id in the $to field so the sender will also get a copy which is not really the right way. I would like to know how to still hide all the address and then not send the mail to the sender.

Please check the code as below:

It works well by sending mail to all the id's(whatever is typed in) and also the sender(which is not needed!!).

Also I would like to know if I have to implement any security method to the mail function. Please let me know how to implement this.
$email = $_REQUEST['email'];
$name = $_REQUEST['name'];
$email1 = $_REQUEST['email1'];
$email2 = $_REQUEST['email2'];
$email3 = $_REQUEST['email3'];
$email4 = $_REQUEST['email4'];
$email5 = $_REQUEST['email5'];
$message = $_REQUEST['message'];
#this will be used for the BCC
$email_ids = "$email1,$email2,$email3,$email4,$email5";
#Will show the sender's id in the From field
$headers = "From: $email" ;
#Will send the mail to sender(which is not required)
$to = "$email";
#Subject with name and email
$subject = "Refered by your friend $name($email)";
mail ($to, $subject, $message, $headers, "Bcc:$email_ids");

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Roger BaklundCommented:
What do you want in the email To header? There must be something there...

The 5. parameter for mail() is additional_parameters. The code you provided does not work for me:

mail ($to, $subject, $message, $headers, "Bcc:$email_ids");

This, however, works:

mail ($to, $subject, $message, $headers."\r\nBcc:$email_ids");
Roger BaklundCommented: for security: You must prevent the evil user from injecting headers, you can do that by removing any occurences of "\r" and "\n" in any of the email addresses.

function clean_email($email) {
  return str_replace(array("\r","\n"),'',$email);

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IgiwwaAuthor Commented:
Hi cxr,
thanks for the replies. Yeah, I understand that I have to mention some id for the To field, but I am thinking if its possible to use one of the "friend's mail id" as the "To" address but others should not see it. OR how generally it works?a copy is always send to the sender or the site owner will have a dedicated id ?

I will implement the security method. thanks again. Is there any other security method?

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IgiwwaAuthor Commented:

I forgot to ask, how to check all the emails(sender/receiver)(i.e. $email, $email1, $email2, $email3..) in the clean_email function?
IgiwwaAuthor Commented:
How about sending an individual email to each user by using "To" field? Is that possible?
From : Sender id
To:friend one id

From : sender id
To: Friend two id.
Roger BaklundCommented:
You can not use one of the "friends" email without letting the others see it, it is just one email, five identical copies are sent. You should use the site owner email or the sender email as a To email in this case.

You can use the clean_email() function like any other PHP function, you must call it for each email address you want to check:
$email = clean_email($_REQUEST['email']);
$email1 = clean_email($_REQUEST['email1']);
$email2 = clean_email($_REQUEST['email2']);
$email3 = clean_email($_REQUEST['email3']);
$email4 = clean_email($_REQUEST['email4']);
$email5 = clean_email($_REQUEST['email5']);

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Roger BaklundCommented:
Yes, you can of course send multiple emails. Use the same procedure as when you are sending one email, just repeat the call to mail() multiple times with different To address. something like this:
if($email1>"") mail($email1, $subject, $message, $headers);
if($email2>"") mail($email2, $subject, $message, $headers);
if($email3>"") mail($email3, $subject, $message, $headers);
if($email4>"") mail($email4, $subject, $message, $headers);
if($email5>"") mail($email5, $subject, $message, $headers);

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IgiwwaAuthor Commented:
Thanks a lot!
Everything works fine.
Just wondering, if there is any other security method we have to implement OR  please direct me to a site which will have more info about this.
Roger BaklundCommented:
I assume you are asking about security related to this email function, and not to your web site as such.

Removing \r (carriage return, ascii 13) and \n (linefeed, ascii 10) from any user input that goes into the $header is the most important step. Now that you do not use BCC, the user input is NOT put into the header, this elimintates the need for the clean_email() function. But it does not do any harm, so it's ok to use it even if the email address is only used in the To field of the email (first parameter to the mail() function).

Modern email clients can handle html in email. To send html in email, you need to use special headers (MIME and Content-type:text/html). If those headers are not there, it is not a html email, even if it contains html code. The html code will simply be visible in the email, like when you "View source" on a web page. However, there COULD be that some (badly coded) email client would detect the occurence of html in the mail, and render the html. I don't know of any such email client, and if there is one, it is faulty. If such an email client exists, your mail function could be abused by sending hostile html emails to such clients.

To eliminate the remote possibility of this, you can remove any html from the $message. This can be done with a builtin PHP function called strip_tags(). It is not common to do this, some will say it is bordering on paranoia, but if you want to be extra safe, you can do it.

$message = strip_tags($_REQUEST['message']);

This is not security related, but you should also use the wordwrap() function so that no line in the message is longer than 78 characters. No modern email clients will have any problem with longer lines, but the spec (rfc 2822) says that the line SHOULD be no more than 78 characters.

$message = wordwrap($message,78);

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IgiwwaAuthor Commented:
thanks a lot for explaining this!
will implement these security code.
thanks again!
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