Add a MAIL_ENCODING parameter in the phpmailer plugin to eventually switch to 7bit for old Exchange+Outlook configs.

(cherry picked from commit 98eebeb)

Author: cdujeu

core/src/plugins/mailer.phpmailer-lite/class.PhpMailLiteMailer.php

@@ -58,7 +58,7 @@ protected function sendMailImpl($recipients, $subject, $body, $from = null, $ima
         $mail->WordWrap = 50;                                 // set word wrap to 50 characters
         $mail->IsHTML(true);                                  // set email format to HTML
         $mail->CharSet = "utf-8";
-        $mail->Encoding = "quoted-printable";
+        $mail->Encoding = $this->getFilteredOption("MAIL_ENCODING");
         foreach ($images as $image) {
             $mail->AddEmbeddedImage($image["path"], $image["cid"], '', 'base64', 'image/png');
         }

core/src/plugins/mailer.phpmailer-lite/manifest.xml

@@ -4,6 +4,7 @@
     <server_settings>
         <param name="MAILER" type="select" choices="sendmail|sendmail,mail|mail" label="CONF_MESSAGE[Mailer]" description="CONF_MESSAGE[Php mailer to use (see phpmail-lite documentation).]" mandatory="true" default="sendmail"/>
         <param name="SENDMAIL_PATH" type="string" label="CONF_MESSAGE[Sendmail Path]" description="CONF_MESSAGE[Path to sendmail if not the default one]" mandatory="true" default="/usr/sbin/sendmail"/>
+        <param name="MAIL_ENCODING" type="select" choices="quoted-printable,8bit,7bit,binary,base64" label="CONF_MESSAGE[Mails Encoding]" description="CONF_MESSAGE[Content encoding of the email. Default value should be ok for most configurations. Some specific Windows Exchange + Outlook combination may require switching to 7bit.]" default="quoted-printable"/>
     </server_settings>
     <class_definition filename="plugins/mailer.phpmailer-lite/class.PhpMailLiteMailer.php" classname="PhpMailLiteMailer"/>
     <client_settings>