diff --git a/api/src/Mail.php b/api/src/Mail.php
index 33c388adea..b107fe8d99 100644
--- a/api/src/Mail.php
+++ b/api/src/Mail.php
@@ -7031,7 +7031,7 @@ class Mail
 				$needsReplacement = false;
 				foreach((array)$value as &$val)
 				{
-					if (strlen($val) > 998)
+					if (strlen($val)+ strlen($header) > 900)
 					{
 						$needsReplacement = $needsFix = true;
 					}