diff --git a/frappe/email/receive.py b/frappe/email/receive.py
index 39bdede07c..c1be68803c 100644
--- a/frappe/email/receive.py
+++ b/frappe/email/receive.py
@@ -283,7 +283,7 @@ class EmailServer:
 
 	def get_email_seen_status(self, uid, flag_string):
 		"""parse the email FLAGS response"""
-		if not flag_string:
+		if not flag_string or not isinstance(flag_string, str | bytes):
 			return None
 
 		flags = []