Issue #131737 by malc0mn, pillarsdotnet, xjm, scor, v1nce, Pancho, mrfelton....

Issue #131737 by malc0mn, pillarsdotnet, xjm, scor, v1nce, Pancho, mrfelton. et al: Ensure that the Return-Path is set when sending mail on both Windows and non-Windows systems.

core/modules/system/system.mail.inc

@@ -65,26 +65,47 @@ public function mail(array $message) {
     // For headers, PHP's API suggests that we use CRLF normally,
     // but some MTAs incorrectly replace LF with CRLF. See #234403.
     $mail_headers = join("\n", $mimeheaders);
-    if (isset($message['Return-Path']) && !ini_get('safe_mode')) {
-      $mail_result = mail(
-        $message['to'],
-        $mail_subject,
-        $mail_body,
-        $mail_headers,
-        // Pass the Return-Path via sendmail's -f command.
-        '-f ' . $message['Return-Path']
-      );
+
+    // We suppress warnings and notices from mail() because of issues on some
+    // hosts. The return value of this method will still indicate whether mail
+    // was sent successfully.
+    if (!isset($_SERVER['WINDIR']) && strpos($_SERVER['SERVER_SOFTWARE'], 'Win32') === FALSE) {
+      if (isset($message['Return-Path']) && !ini_get('safe_mode')) {
+        // On most non-Windows systems, the "-f" option to the sendmail command
+        // is used to set the Return-Path. There is no space between -f and
+        // the value of the return path.
+        $mail_result = @mail(
+          $message['to'],
+          $mail_subject,
+          $mail_body,
+          $mail_headers,
+          '-f' . $message['Return-Path']
+        );
+      }
+      else {
+        // The optional $additional_parameters argument to mail() is not
+        // allowed if safe_mode is enabled. Passing any value throws a PHP
+        // warning and makes mail() return FALSE.
+        $mail_result = @mail(
+          $message['to'],
+          $mail_subject,
+          $mail_body,
+          $mail_headers
+        );
+      }
     }
     else {
-      // The optional $additional_parameters argument to mail() is not allowed
-      // if safe_mode is enabled. Passing any value throws a PHP warning and
-      // makes mail() return FALSE.
-      $mail_result = mail(
+      // On Windows, PHP will use the value of sendmail_from for the
+      // Return-Path header.
+      $old_from = ini_get('sendmail_from');
+      ini_set('sendmail_from', $message['Return-Path']);
+      $mail_result = @mail(
         $message['to'],
         $mail_subject,
         $mail_body,
         $mail_headers
       );
+      ini_set('sendmail_from', $old_from);
     }
     return $mail_result;
   }