Postfix Ignores PHP mail() function

mail($to, $subject, $message, $headers,'From: ' . $fromname . ' <'.$from.'>', "-f $from -r mybounceemail@example.com");

Cannot work as mail() only accepts 5 parameters: bool mail ( string $to , string $subject , string $message [, string $additional_headers [, string $additional_parameters ]] )

For me both

mail($to, $subject, $message, null, "-r sender@example.com");
mail($to, $subject, $message, 'Name <something@example.com>', "-r sender@example.com");

work (I don't have any additional restrictions in postfix which might rewrite senders). Also make sure that the sender is properly formatted (no spaces or whatsoever).

However, I recommend to adjust the sendmail_path setting in your php.ini to include the "-r mybounceemail@example.com" parameter.

If it doesn't work for you, you should post the mail headers here and check your log files for warnigns/errors.

PS: Please make sure you don't pass user entered data directly to mail(), because if users can insert newlines (such as \nCC: something@example.com in subject, to mail or from mail) your server might be used for spamming.

You could let the Postfix do its job rewriting headers and adding proper From: addresses. For this, Postfix has sender_canonical_maps.

Let's say your web server (or a process manager) runs under user named username, and you want to have support@example.com in the From: header of your emails instead of unclear username@servername.example.com. Then, canonical map would contain:

#/etc/postfix/canonical
username support@example.com

Configuring Postfix to use it can't be easier:

postmap /etc/postfix/canonical
postconf -e sender_canonical_maps=hash:/etc/postfix/canonical

Other option is to tell postfix to mark all emails send from you server as send from support@example.com by means of luser_relay:

postconf -ev luser_relay=support@example.com

If you can't do it, quite possible someone already did this for you, but did that wrong. That could be a reason why you can't change From: address since it is being forcedly overwritten by Postfix.

You've got the header argument in your mail() call twice and thus, your $additional_parameters argument isn't being used because it's the 6th argument in a function that only accepts 5. You should instead move the header to be included with the rest of your headers:

//Be mindful to protect from email injection attacks.
$fromname = str_replace("\n", "", $fromname);
$from = str_replace("\n", "", $from);

//This assumes that $headers is already set, containing your other headers
$headers .= 'From: ' . $fromname . ' <'.$from.">\n";

mail($to, $subject, $message, $headers, "-f $from -r mybounceemail@example.com");

Using this, I would expect that your 5th argument is now redundant and could be simplified to:

$fromname = str_replace("\n", "", $fromname);
$from = str_replace("\n", "", $from);

$headers .= 'From: ' . $fromname . ' <'.$from.">\n";

mail($to, $subject, $message, $headers);