Merge branch 'master' into 6.0

# Conflicts:
#	.gitignore
#	VERSION
#	src/PHPMailer.php
#	src/POP3.php
#	src/SMTP.php

.gitignore

@@ -2,6 +2,6 @@ docs/*
 !docs/README.md
 test/message.txt
 test/testbootstrap.php
-*.pem
+test/*.pem
 build/
 vendor/

changelog.md

@@ -38,6 +38,14 @@ This is a major update that breaks backwards compatibility.
 * `Extras` classes have been removed - use packages from [packagist.org](https://packagist.org) instead
 * Better handling of automatic transfer encoding switch in the presence of long lines
 
+## Version 5.2.16 (June 6th 2016)
+* Added DKIM example
+* Fixed empty additional_parameters problem
+* Fixed wrong version number in VERSION file!
+* Improve line-length tests
+* Use instance settings for SMTP::connect by default
+* Use more secure auth mechanisms first
+
 ## Version 5.2.15 (May 10th 2016)
 * Added ability to inject custom address validators, and set the default validator
 * Fix TLS 1.2 compatibility

examples/DKIM.phps

@@ -0,0 +1,38 @@
+<?php
+/**
+ * This example shows how to use DKIM message authentication with PHPMailer.
+ * There's more to using DKIM than just this code - check out this article:
+ * @link https://yomotherboard.com/how-to-setup-email-server-dkim-keys/
+ * See also the DKIM code in the PHPMailer unit tests,
+ * which shows how to make a key pair from PHP.
+ */
+
+require '../PHPMailerAutoload.php';
+
+//Create a new PHPMailer instance
+$mail = new PHPMailer;
+//Set who the message is to be sent from
+$mail->setFrom('from@example.com', 'First Last');
+//Set an alternative reply-to address
+$mail->addReplyTo('replyto@example.com', 'First Last');
+//Set who the message is to be sent to
+$mail->addAddress('whoto@example.com', 'John Doe');
+//Set the subject line
+$mail->Subject = 'PHPMailer DKIM test';
+//This should be the same as the domain of your From address
+$mail->DKIM_domain = 'example.com';
+//Path to your private key file
+$mail->DKIM_private = 'dkim_private.pem';
+//Set this to your own selector
+$mail->DKIM_selector = 'phpmailer';
+//If your private key has a passphrase, set it here
+$mail->DKIM_passphrase = '';
+//The identity you're signing as - usually your From address
+$mail->DKIM_identity = $mail->From;
+
+//send the message, check for errors
+if (!$mail->send()) {
+    echo "Mailer Error: " . $mail->ErrorInfo;
+} else {
+    echo "Message sent!";
+}

src/PHPMailer.php

@@ -364,7 +364,7 @@ class PHPMailer
 
     /**
      * DKIM Identity.
-     * Usually the email address used as the source of the email
+     * Usually the email address used as the source of the email.
      * @var string
      */
     public $DKIM_identity = '';
@@ -1393,7 +1393,9 @@ class PHPMailer
         }
         $to = implode(', ', $toArr);
 
-        if (empty($this->Sender)) {
+        $params = null;
+        //This sets the SMTP envelope sender which gets turned into a return-path header by the receiver
+        if (!empty($this->Sender)) {
             $params = ' ';
         } else {
             //A space after `-f` is optional, but there is a long history of its presence