diff --git a/smtp2slack4qnap.py b/smtp2slack4qnap.py
index 79d7a71..c5217b9 100644
--- a/smtp2slack4qnap.py
+++ b/smtp2slack4qnap.py
@@ -7,6 +7,7 @@
 # generate self-signed cert (better than nothing):
 # openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 3650 -nodes -subj '/CN=localhost'
 
+import os
 import ssl
 import asyncio
 from aiosmtpd.controller import Controller