SMTP server response: 501 Must specify to address <address>

Cannot understand why I am getting this error - both to & from email addresses are valid (I use them daily) so cannot figure out how this is happening - any help would be appreciated.

NOTE: This is working in production but is throwing errors in dev. I have stricter config in dev. NOTE: I am testing locally on PC using smtp4dev

    $to = 'myemail@mydomain.com.au';
    $cc = 'myemail@mydomain.com.au';
    $from = 'myemail@mydomain.com.au';
    $filename = 'Invoice#'.$order_id.'.pdf';
    $message = file_get_contents(ROOT_DIR.'admin/include/email-body.html');
    $content = chunk_split(base64_encode($pdf_file));
    $uid = md5(uniqid(time()));

    $headers  = 'MIME-Version: 1.0' . "\r\n";
    $headers .= 'To: '. $to . "\r\n";
    $headers .= 'Cc: '. $cc . "\r\n";
    $headers .= 'From: '. $from . "\r\n";
    $headers .= "Content-Type: multipart/mixed; boundary=\"".$uid."\"\r\n\r\n";
    $headers .= "This is a multi-part message in MIME format.\r\n";
    $headers .= "--".$uid."\r\n";
    $headers .= "Content-type:text/html; charset=iso-8859-1\r\n";
    $headers .= "Content-Transfer-Encoding: 7bit\r\n\r\n";
    $headers .= $message."\r\n\r\n";
    $headers .= "--".$uid."\r\n";
    $headers .= "Content-Type: application/pdf; name=\"".$filename."\"\r\n";
    $headers .= "Content-Transfer-Encoding: base64\r\n";
    $headers .= "Content-Disposition: attachment; filename=\"".$filename."\"\r\n\r\n";
  开发者_如何学JAVA  $headers .= $content."\r\n\r\n";
    $headers .= "--".$uid."--";

    if (mail($to, $subject, $message, $headers)) {
      print "SUCCESS";
    } else {
      print "FALIED";
    }

Here is the result if I print the variables on the mail() line:

mail(<myemail@mydomain.com.au>, Company - Invoice#12451, "",
MIME-Version: 1.0 
To: <myemail@mydomain.com.au> 
Cc:
From: Customer Service <myemail@mydomain.com.au> 
Content-Type: multipart/mixed;
boundary="2c88ff549e67c83e7a6e3df0bffe9dc9"

This is a multi-part message in MIME format.
--2c88ff549e67c83e7a6e3df0bffe9dc9 Content-type:text/html;
charset=iso-8859-1 Content-Transfer-Encoding: 7bit

---> html message body stripped <---


--2c88ff549e67c83e7a6e3df0bffe9dc9 Content-Type: application/pdf;
name="Invoice#12451.pdf" Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="Invoice#12451.pdf"

--> pdf attachment stripped <--


--2c88ff549e67c83e7a6e3df0bffe9dc9--)

(Author of smtp4dev here)

This is an updated answer - I couldn't originally reproduce the problem with the code you posted, but I noticed that your second bit of output shows that sometimes you don't have a CC address.

This code reproduces the problem and results in the 501 error.

<?php
    $to = 'myemail@mydomain.com.au';   
    $cc = '';  
    $from = 'myemail@mydomain.com.au';
    $headers .= 'To: '. $to . "\r\n";
    $headers .= 'Cc: '. $cc . "\r\n";
    $headers .= 'From: '. $from . "\r\n";

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

On Windows the PHP mail function looks at the message headers for TO/CC addresses and converts each header to a SMTP RCPT TO command. Unfortunately it does this even if the header has no value:

220 localhost smtp4dev ready
HELO Computer
250 Nice to meet you
MAIL FROM:<myemail@mydomain.com.au>
250 Okey dokey
RCPT TO:<myemail@mydomain.com.au>
250 Recipient accepted
RCPT TO:<>
501 Must specify to address <address>
QUIT
221 See you later aligator

The fix is therefore is that you need to not include the CC: header at all if you don't have a CC address to send to:

<?php
    $to = 'myemail@mydomain.com.au';   
    $cc = '';  
    $from = 'myemail@mydomain.com.au';
    $headers .= 'To: '. $to . "\r\n";

    if ($cc) {
        $headers .= 'Cc: '. $cc . "\r\n";
    }
    $headers .= 'From: '. $from . "\r\n";

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

This worked fine for me.

smtp4dev is just a bit pickier than most actual SMTP relays with regard to the format of the recipient.

Doesn't work:

helo me
mail from: me@here.com
rcpt to: somebody@mydomain.tld

Works:

helo me
mail from: me@here.com
rcpt to: <somebody@mydomain.tld>