diff --git a/api/src/Mail.php b/api/src/Mail.php
index ca42b044d0..cb9fdae918 100644
--- a/api/src/Mail.php
+++ b/api/src/Mail.php
@@ -7029,7 +7029,7 @@ class Mail
 			foreach($headers->toArray() as $header => $value)
 			{
 				$needsReplacement = false;
-				foreach((array)$value as &$val)
+				foreach((array)$value as $val)
 				{
 					if (strlen($val)+ strlen($header) > 900)
 					{