diff --git a/api/src/Mail.php b/api/src/Mail.php
index 5642fba221..0a7c08eb9e 100644
--- a/api/src/Mail.php
+++ b/api/src/Mail.php
@@ -5574,12 +5574,12 @@ class Mail
 	 * @param string/int $_partID = '' , the partID, may be omitted
 	 * @param string $_folder folder to work on
 	 * @param boolean $_stream =false true: return a stream, false: return string, stream suppresses any caching
-	 * @return string the message body
+	 * @return ?string the message body or null if $_uid or $_partID not found
 	 */
 	function getMessageRawBody($_uid, $_partID = '', $_folder='', $_stream=false)
 	{
 		static $rawBody;
-		$body = [];
+		$body = null;
 		if (empty($_folder)) $_folder = $this->sessionData['mailbox']?: $this->icServer->getCurrentMailbox();
 		$_uid = !(is_object($_uid) || is_array($_uid)) ? (array)$_uid : $_uid;
 
diff --git a/mail/inc/class.mail_ui.inc.php b/mail/inc/class.mail_ui.inc.php
index 08dda2556f..c67f8b7b5c 100644
--- a/mail/inc/class.mail_ui.inc.php
+++ b/mail/inc/class.mail_ui.inc.php
@@ -2965,7 +2965,7 @@ $filter['before']= date("d-M-Y", $cutoffdate2);
 				$file = $tmp_file;
 			}
 
-			if (!($fp = Vfs::fopen($file,'wb')) || !fwrite($fp,$message))
+			if (!is_string($message) || !($fp = Vfs::fopen($file,'wb')) || !fwrite($fp,$message))
 			{
 				$res['msg'] = lang('Error saving %1!',$file);
 				$res['success'] = false;