diff --git a/lib/moodlelib.php b/lib/moodlelib.php
index ec54c3a3ca7..26425261c7d 100644
--- a/lib/moodlelib.php
+++ b/lib/moodlelib.php
@@ -5884,7 +5884,16 @@ function email_to_user($user, $from, $subject, $messagetext, $messagehtml = '',
         } else {
             require_once($CFG->libdir.'/filelib.php');
             $mimetype = mimeinfo('type', $attachname);
-            $mail->addAttachment($CFG->dataroot .'/'. $attachment, $attachname, 'base64', $mimetype);
+
+            $attachmentpath = $attachment;
+
+            // If the attachment is a full path to a file in the tempdir, use it as is,
+            // otherwise assume it is a relative path from the dataroot (for backwards compatibility reasons).
+            if (strpos($attachmentpath, $CFG->tempdir) !== 0) {
+                $attachmentpath = $CFG->dataroot . '/' . $attachmentpath;
+            }
+
+            $mail->addAttachment($attachmentpath, $attachname, 'base64', $mimetype);
         }
     }
 
diff --git a/lib/tests/messagelib_test.php b/lib/tests/messagelib_test.php
index 6f4bd2797eb..20b602fbe9a 100644
--- a/lib/tests/messagelib_test.php
+++ b/lib/tests/messagelib_test.php
@@ -231,6 +231,11 @@ class core_messagelib_testcase extends advanced_testcase {
         $email = reset($emails);
         $this->assertTrue(strpos($email->body, 'Content-Disposition: attachment;') !== false);
         $this->assertTrue(strpos($email->body, 'emailtest.txt') !== false);
+
+        // Check if the stored file still exists after remove the temporary attachment.
+        $storedfileexists = $fs->file_exists($filerecord['contextid'], $filerecord['component'], $filerecord['filearea'],
+                                             $filerecord['itemid'], $filerecord['filepath'], $filerecord['filename']);
+        $this->assertTrue($storedfileexists);
     }
 
     /**
diff --git a/message/output/email/message_output_email.php b/message/output/email/message_output_email.php
index cfe9fd460cf..722aea1db4c 100644
--- a/message/output/email/message_output_email.php
+++ b/message/output/email/message_output_email.php
@@ -77,8 +77,7 @@ class message_output_email extends message_output {
             } else {
                 // Copy attachment file to a temporary directory and get the file path.
                 $attachment = $eventdata->attachment->copy_content_to_temp();
-                // Function email_to_user() adds $CFG->dataroot to file path, so removing it here.
-                $attachment = str_replace($CFG->dataroot, '', $attachment);
+
                 // Get attachment file name.
                 $attachname = clean_filename($eventdata->attachname);
             }
@@ -88,7 +87,9 @@ class message_output_email extends message_output {
                                 $eventdata->fullmessagehtml, $attachment, $attachname);
 
         // Remove an attachment file if any.
-        @unlink($attachment);
+        if (!empty($attachment) && file_exists($attachment)) {
+            unlink($attachment);
+        }
 
         return $result;
     }